Home:Rat Behavior: Glossary

Glossary of rat behavior terms

Informal, illustrated definitions of rat behavior terms

INDEX

Allogroom, head and body: One rat grooms the other, frequently around the neck or head (especially the eyes, mouth, chin and ears). Somewhat less frequently, one rat may groom the flanks of another.

Allogrooming of the neck occurs in an agonistic context and is called aggressive neck grooming.  Grooming consists of rapid little nibbles, in one spot or moving slowly to one side.  Slow motion video analysis reveals that the groomer seizes folds of neck skin between his teeth (Miczek and Boer 2004).  The groomed rat remains immobile, and may even be pushed into different positions.  The groomed rat may peep or squeak softly.  Any sudden movement by the groomed rat may trigger a bite and a kick from the rear legs of the groomer (Miczek and Boer 2004).

Grooming of the head and neck may be an olfactory investigation of the sebum from the back of the animal.

Barber: Excessive grooming in which the fur is nibbled off. Rats may barber each other, in which case frequent areas of barbering and subsequent bald spots on other rats are the head, face, neck and shoulders. Dominant rats may barber subordinates (e.g. Bresnahan 1983). Lactating mothers may have barbered stomachs, either as the result of nibbling by the babies once their teeth have erupted, or by the dam herself in response to irritation from the nursing.

Self-barbering is also found in non-lactating rats, in which case the rat may nibble off fur from its forearms and chest. Barbering is sometimes caused by Demodex mites, or as a result of mutual grooming when the rats' diet contains more than 20% fat. Other possible causes include skin ulcers (pyoderma), other external parasites, genetic disorders, caloric or protein deficiencies, abrasion on rough surfaces, hormonal imbalances, chronic renal disease, ringworm (dermatophytosis), and intensive breeding (Harkness and Wagner 1995).

Behavioral Estrus (female behavior in heat): Phase of the female rat's ovarian cycle during which she displays reproductive behavior. Behavioral estrus corresponds to vaginal proesturs, the 12 hour period before ovulation.

During behavioral estrus, the female solicits the male to prompt him into mounting her. She darts towards him and runs or hops away. She may repeat this approach-retreat sequence several times, sometimes wiggling her ears. She may also pause near him or run by him, and may intercept him in his pursuit of another female. The male finds these solicitation behaviors very attractive, and follows the female. If he mounts her, the pressure he exerts on her flanks, lower back, and anogenital area triggers lordosis, the female mating posture (Nelson 1995).

Belly-groom or "power grooming": One rat grooms a recumbent rat's belly. May be an attempt to reach the nape, which is the goal of play fighting. See also "Belly-up roll" and allogrooming.

Belly-up roll (pin): Juvenile-type defense tactic in which one rat rolls onto his back before another, sometimes after receiving a nip or bite on the rump. The top rat may then step on the supine rat, sometimes orienting himself perpendicular to the long axis of the supine rat (thus avoiding the whiskers), and pinning him down. The top rat may groom the supine rat's belly (see also belly-groom, or "power groom"), perhaps as an attempt to gain access to the nape or rump. Rolling on one's back tends to prevent further attack for several reasons: play fighting is directed at the nape, and serious offensive bites are directed at the lower back and flanks, so a roll hides these areas. Also, the rolled rat becomes motionless, and motion is an important stimulus for attack (Thor et al. 1981). Lastly, the recumbent rat may track his opponent's face with his teeth and whiskers, which may actively inhibit attacks as well (Blanchard and Blanchard 1977).

So, the belly-up roll is probably not a signal of submission or defeat that inhibits further attack, because the attaker may continue to press his attack. The belly-up roll is instead a defensive strategy: the subordinate rat can escape being bitten insofar as he can interpose his belly between the attacker and his own vulnerable target areas of rump and nape.

Bite: Piercing contact with the teeth that scratches or breaks the skin. Damage ranges from a superficial scratch to a deep puncture to a slash. For a deep bite, the rat touches the object with its upper incisors and brings the lower incisors powerfully upward. Rats are also capable of voluntarily separating their lower incisors into a "V" shape that may increase the damage from a bite.

Social biting: In a social context, rats may bite each other, particularly during fights. Offensive bites tend to be directed at the lower back and flanks. Defensive bites tend to be directed at the face. Defensive bites are sometimes delivered in a lunge-and-bite sequence. The bite to the head is characteristic of hurt, frightened, or defensive rats.

Note that lunging bites directed at the face may also be used offensively, especially by females toward intruders (DeBold and Miczek 1981). Check out RatRaisins, Inc. for more discussion of rat bites.

Predatory biting: During a predatory sequence, rats may also bite their prey with their incisors and kill it. For example, rats may bite the head, neck or upper back of mice (Hsuchou et al. 2002). Rats may bite the heads off of crickets prior to eating them.

Food biting: While eating, rats bite off small chunks of food with their incisors. The food is passed back into the mouth where it can be chewed between the molars.

Box: Two rats stand on their hind legs face to face and nearly nose to nose, and push or paw at each other with their front legs and paws, usually around the head, neck, shoulders and front legs of their opponent. In high intensity boxing the rats stand erect on their hind feet and rapidly push, paw, and grab at each other. In low intensity boxing the rats squat on their haunches and paw at each other gently. If no contact is involved, the encounter is a nose-off. Boxing is a defensive strategy: as long as the subordinate rat maintains whisker-to-whisker contact, the dominant rat cannot bite his rump. The dominant rat may respond to the boxing tactic with a sidle (Blanchard et al. 1977).

Bound (ricocheting jump): Rat advances with leaps: it pushes off with both hind feet, lands on both front feet, brings forward the hind feet and pushes off again. The rat spends 3/4 of its time in the air: in one beat, the forefeet hit the ground followed quickly by the hind feet, which push the rat into the air, and three beats later the forefeet hit the ground again. The back arches when the hind feet are brought forward, making bounding very conspicuous. The rat may also thump at each bound when it hits the ground.

Brux : Soft, repetitive grinding of the incisors against each other. Serves the sharpen the incisors and may be given in times of relaxation or stress (Rosales et al 2002, Pohto 1979). Also see chatter.

To read more about bruxing and to hear rat sound samples, go to the Norway Rat Vocalizations Page.

Caching, or Stashing: The rat picks up a food item in its mouth, runs elsewhere, and deposits the food item. The rat frequently leaves the item there and returns for another load. The place a rat chooses to cache food in is usually a protected, hidden or semi-hidden location, such as a nestbox, a dead-end passage, or a dark corner.

Cephalocaudal groom ("CCG"): Grooming sequence of face and body (common to all rodents). The rat starts by licking the paws, then rubs them over the head. This is followed by licking and rubbing the side of the body, the anogenital region, and the tail. The sequence may be anywhere from loosely organized to very stylized, performed in a similar or identical fashion each time. In rats, most sequences appear to be loosely organized. The grooming sequence may be interrupted at any point, and it seems that rats usually stop before grooming their tails.

Chase, or pursuit: Running behavior in which a rat pursues a target individual. If the chase occurs in a social context, the pursuer may deliver a nip to the fleeing rat's rump if he gets close enough. Rats may also pursue prey.

Chatter (teeth-chatter): Repetitive grinding of the incisors against each other. May be given during intense agonistic encounters, and may represent an internal conflict (dual activation) of attack and flight tendencies (Lammers et al. 1988). May be louder and may contain more sharp crackling sounds than bruxing in a relaxed context.

To read more about chattering and to hear rat sound samples, go to the Norway Rat Vocalizations Page.

Chew (mastication): Grinding and shredding of food between the molars. The lower jaw is in the back position, such that the molars are in contact with each other and the incisors are not. Chewing is involved in processing food prior to ingestion, and is quite different from gnawing. For details on the exact biomechanics of chewing, see Weijs (1975); Weijs and Dantuma (1975).

Climb: Vertical locomotion up or down a vertical surface. Rats may scale just about any vertical or slanted surface with a sufficient handhold. They use both forefeet (pull) and hind feet (push) to grasp footholds and haul themselves up. They may use their claws if they can't use their toes, as when climbing a screen or fabric. Rats climb up more easily then they descend. They descend head first, and appear to have some difficulty controlling their weight and speed on descent. A rat may start a descent and may then jump or fall the rest of the way.

Crawl: Ineffecient, nonpostural gait shown by baby rats between days 3 and 10.

Crawl-over: One rat approaches the flank side of another rat and maintains close body contact as it crawls over the other animal. Urine marks are deposited during the crawl-over, but not all crawl-overs are accompanied with urine marking. There appears to be no favored body part to mark, urine is distributed over most of the back (Taylor et al. 1987).

Communal nesting (nest sharing): two or more females combine their litters in a single nest and raise them together. The mothers may be related or unrelated, and the litters may be the same or different ages. Often includes communal nursing.

For more, see article entitled Communal nesting and nursing in Norway rats.

Communal nursing (allonursing): the sharing of milk with the young of another mother.

For more, see article entitled Communal nesting and nursing in Norway rats.

Dig: Rats dig by pulling handfulls of dirt backwards with their front paws, making a pile under their stomachs. Sometimes the rat uses its whole forebody to pull a load backwards. Periodically they clear the accumulated pile by kicking it backwards with their hind feet. Rats may clear tunnels by pushing dirt with their forepaws and head.

Dorsal Immobility, or transport immobility response: Freezing or "going limp" behavior that occurs when rats are picked up by the scruff of the neck. The response is triggered by constriction of the skin at the nape (Mileikovsky and Nozdrachev 1997). Dorsal immobility is seen primarily in juveniles when their mother picks them up and transports them from place to place (e.g. retrieving pups back to the nest) (Wilson and Kaspar 1994). Going limp probably helps the mother carry the baby, and the dorsal immobility response is seen in the juveniles of many different altricial species. The response persists into adulthood in rats, as adult rats may continue to freeze when picked up by the scruff (Webster 1981).

Drag (another rat): A rat graps another rat's skin in its teeth and attempts to pull the rat in a particular direction.

Dragging may be seen in mother rats. Price and Belanger (1977) examined the behavior of mother rats toward intruders and found that 33% of females dragged or pulled intruders, usually toward the nest. The mother rats targeted the neck 61.4% of the time, the side 28.3% of the time, the tail 8.7% of the time, and the ear 1.6% of the time. Dragging adult rats may be a component of maternal aggression.

Wiesner and Sheard (1933) observed that lactating female rats may drag their mates and adult offspring toward the nest. Lactating rats may even drag young rabbits or kittens as well. This dragging tends to decrease as lactation wanes, which suggests that dragging is linked with normal pup-carrying. Adult rats may simply be a "supernormal" stimulus for the retrieval response, and the mother may drag them because they are too big to be lifted and carried.

Drink: Most domestic rats drink from water bottles, licking the water off the metal ball at the end of the waterspout. Rats may also lap standing water from a dish.

Ear wiggle: Female vibrates her ears rapidly. Ear wiggling is part of a suite of solicitation behaviors in which the female initiates and maintains mounting behavior by the male. Ear wiggling occurs when the female is in behavioral estrus, about every 4-5 days.

Eye-boggle (eyeboggle, boggle): Eyeball vibrates rapidly in and out of the socket. Occurs during high-intensity bruxing (soft, repetitive grinding of the incisors). The rat's masseter muscle, which passes through the eye socket behind the eyeball, moves the jaw rapidly up and down during bruxing. When bruxing is intense, the contractions of the masseter vibrate the eye in and out of the socket in time with the incisor grinding. Usually considered to indicate pleasure and contentment.

Feed (eat): Consumption of food. Rat takes bites out of food item with its incisors. The morsel of food is then passed deeper into the mouth where it is chewed between the molars and finally swallowed.

Fight, or wrestle: This is an escalated form of conflict, in which two rats wrap around each other into a tight ball, rolling around together and biting, frequently shrieking. According to Blanchard et al. 1975, the attacking rat jumps or lies across the back of his opponent and attempts to bite the opposite flank.

Flank Mark: Flank marking is a scent marking behavior involved in olfactory communication, in which scent from the flank (presumably from the flank sebaceous glands, Ebling 1963) is rubbed onto objects in the environment. Typically, the rat leans sideways into a vertical structure (like a wall or the edge of a burrow entrance) and pushes its side against the surface while pulling itself forward. Males flank mark more than females. Flank marking tends to be performed in familiar environments (Peden and Timberlake 1990).

Flight: One rat runs away from the other, the second rat may or may not pursue.

Forequarter pivot: Adult defense tactic, in which the defending rat stands on its hind legs and pivots its forequarters to face the attacker, but leaves its hindquarters in contact with the ground. The forequarter pivot enables the rat to launch a counterattack. The more juvenile defense is the belly-up roll, in which the hindquarters follow the forequarters and the rat ends up on its back.

Gallop: limbs of both sides move nearly in synchrony (e.g. left and right front legs move nearly together, left and right hind legs move nearly together). The gallop is a fast, asymmetric gait, with a period of free-flight (all four limbs off the ground).

In an extreme form the gallop may become a bound or ricocheting jump, in which the forefeet hit the ground, then the hindfeet hit the ground, then three beats later the forefeet hit the ground again (Gambaryan 1974, mentioned in Golubitsky et al. 1999)

Gnaw: The rat pulls its lower jaw forward with its jaw muscles, such that its incisors touch each other and its molars do not. The upper incisors hold the object, and the lower incisors are pulled powerfully upward to cut against it. Gnawing is a rodent's speciality, and their specialized jaw muscles and jaw atriculation give the rodent a very effective, powerful gnawing action. Gnawing is quite different from chewing, which is used to process food prior to ingestion.

Head Bob (sway): Movement of the head up and down or side to side. May precede a jump over a gap. Rats bob their heads in order to gain a sense of visual depth (distance between themselves and a far away object) using motion parallax cues. Albinos may sway more frequently than pigmented rats because albino vision is very poor. For more on depth perception and the vision of pigmented and albino rats, see What do rats see?

Hide: One rat retreats to a safe area, preferably far away from the aggressive rat. He may stay there, sitting quietly for a long time, sometimes up to an hour.

Hiss: Vocalization made during escalated agonistic encounters, typically when rats are very close to or in contact with each other. Such escalated conflicts tend to occur when the rats are confined and cannot escape each other, as escape takes precedence over fighting and hissing. Hisses tend to last about 1 second and have no discrete begining or end, which makes identification of the hissing rat difficult. Hisses also have an ultrasonic component Berg and Baenninger 1973). The two hisses I have heard were emitted by the defensive rat. To read more about rat vocalizations, go to the Norway Rat Vocalizations Page.

Infanticide (pup-killing): Killing the young of one's own species. Infanticide may be followed by cannibalism, but this is not always the case. Infanticide may be committed by mother rats, by unrelated female rats, by unrelated male rats, or by father rats. Each commits infanticide under different conditions and for different reasons.

The targets of infanticide are usually newborn pups. Rarely, older pups may be killed. Newborn pups are usually simply eaten (picked up and consumed like a food item). Older pups tend to be killed by predatory attack (chase, lunge, bite, kill sequence).

To read more about infanticide, visit the Infanticide in Norway rats page.

Kick: May occur when a sidling rat approaches another very closely. The hind foot closest to the second rat kicks out, and may contact the second rat on the flank or higher on the the back.

Offensive kick: The rat's offensive kick looks more like a hind-foot grab which pulls the two rats into a close encounter, perhaps enabling the kicker to position himself just prior to a fight.

Defensive kick: The rat raises a hind foot and uses it to keep off or push away another rat

Lordosis (female arched back): Female mating posture. Female stands immobile, with her back arched downward toward the floor, her rump pushed upward and tail deflected to the side. Her vulva, which normally faces the floor, rotates almost 90 degrees to the vertical, backward-facing position. Without lordosis, copulation would be impossible.

Lordosis is a reflexive behavior that is triggered by a touch on the lower back, flanks, or genital region. The female may also solicit mounting behavior by the male, which in turn triggers lordosis.

Manipulate food (process food): Rats may process their food before consuming it. Processing may include removing a hard cover from a soft, edible center: gnawing the shell off a nut, peeling the skin off a pea. Processing may also include orienting a prey item with the paws until it is positioned correctly: for example, rats rotate crickets until the insect's head points upward, and the rat proceeds to bite off the head, thus killing the prey. Rats further process crickets by pulling off the legs and wings before eating the thorax and head (Ivanco 1996).

Once the food is procesed, the rat typically holds its food by squatting on its hind legs and holding it between the two front paws, or, more rarely, with just one front paw. Rats may also take bites of food directly without holding it up, though the rat may steady a large edible object with a forepaw. This usually happens when a food item is too large to pick up (e.g. chicken bone or corncob), or when the food is pureed (e.g. soup, syrup) or too fine to pick up (e.g. sugar granules).

Maternal aggression: Attacks by a mother rat with a young litter. Typically, such attacks consist of a lunge and bite attack, and are directed at any animal approaching the mother's nest and young. Mothers may also sidle, box and drag intruders. Such attacks may discourage other animals from approaching and possibly harming her offpsring (e.g. predators, unfamiliar rats).

Mount: One rat places its forequarters on another rat's rump from behind. Mounting is the male copulatory position, and is seen when a male mounts a female prior to mating. Mounting is also sometimes seen between rats of the same sex, usually in an aggressive context.

Nestbuild: Rats may drag or carry desirable nesting material in their mouths into their chosen sleeping spot, such as a nestbox or burrow. In captivity they may choose bedding such as fabric pieces, tissue paper, paper towels, toilet paper, and shredded cardboard. Wild rats may use leaves and grass. Rats shred the material into smaller sizes, and line the bottom of their nestbox with it.

Rats build several types of nest:

Nibble: Rats may nibble their own skin or that of other rats with their teeth. Under normal circumstances they do not bite off the fur, but rather appear to be combing the fur with their teeth and nibbling the skin underneath. If nibbling is excessive it may become self-barbering or barbering of another rat.

Nip: Light pinching contact with the teeth, skin unbroken. May elicit a squeak.

Nose-off: Two rats stand immobile, facing each other. The rats may have all four paws on the ground, or may have one or both front paws up (in which case a nose-off may segue into boxing). Sometimes one rat leans in toward the other while the second rat leans away from him (the rat who leans in is usually the dominant rat). Generally, the closer the rats are to each other, the more intense the encounter. The nose-off may be accompanied with the open-mouth tooth display from the subordinate rat. Nose-offs are a defensive strategy: as long as the subordinate rat maintains whisker-to-whisker contact, the dominant rat cannot bite him. Nose-offs may escalate into boxing. The dominant rat may respond to the nose-off or boxing tactics with a sidle (Blanchard et al. 1977).

Nose-offs may escalate into boxing.

Nursing posture: Huddled, crouching posture of a mother rat over her offspring, which allows them to nurse and provides them with protection and warmth. The nursing posture may also be performed by non-lactating females and even males who have been repeatedly exposed to foster pups.

Open-mouth tooth display: Facial expression in which the mouth is open, revealing the base or all of the bottom incisors. The more intense the expression, the wider the mouth and the more you can see the teeth. In a very intense version (seen during a nose-off), the mouth is wide open and lower incisors are spread apart into a "V" shape, and the rat may squeak or hiss. Also, the forehead fur appears flattened and ears may be pulled slightly down and rotated forward. This "flat foreheaded" look was useful to me in the past, with my now deceased female rat Paint, because it was a good predictor of an impending lunge-and-bite onto my hand.

Overmark: Deposit of a scent mark over the scent mark of another rat. The topmost scent mark is known as the top-scent, and the animal who puts it there is called the top-scent-male or top-scent-female.

Peep: Brief (0.1 sec) high pitched note that sweeps steeply upward in pitch. Sounds like a soft "bwip." Heard during head and body allogrooming. To read more about peeps and listen to peep samples, go to the Norway Rat Vocalizations Page.

Pica: The consumption of non-nutritive substances like clay, kaolin (a type of clay), or even bedding. Pica is the rat's response to nausea, as rats cannot vomit.

Piloerection ("poofing"): The rat's body hair stands on end. May occur when the rat is cold, or when stressed, such as during or after an intense altercation.

Predatory attack: Sequence of behaviors used to hunt and kill prey. A common sequence includes: detection of prey --> chase --> bite --> kill --> manipulate --> eat. More on predation by rats.

Pup retrieval: Carrying behavior in which a mother rat picks up a straying pup in her mouth, usually by the neck, and brings it back to the nest. May be facilitated by the pup's transport immobility response.

Push: May occur when a sidling rat makes physical contact with another rat. Using the broadside of its body, the sidling rat presses against the second rat. The sidling rat may tuck his head town, sometimes as far down as between his front paws (possibly to protect it), or under the second rat (possibly to gain leverage). The second rat may reciprocate, such that both rats push against each other. Alternatively, the second rat may be pushed back. If the encounter happens on a ledge, the pushing rat may maneuver the second rat off the ledge.

Scratch: Rats may raise a hind foot and scratch themselves, usually with rapid movements of the hind foot and claws. They can reach their head (eyes, ears etc.), neck, front leg and side with their hind foot.

Shriek: Loud scream that covers many frequencies at once, from 0.2 to 20 kHz and perhaps up into ultrasound. Heard during fights, or when rat is in pain, or in strong protest. To read more about shrieks and to hear shriek samples, go to the Norway Rat Vocalizations Page.

Sidle (lateral display, crab walk, crowd): Threatening posture in which one rat (usually but not always the dominant one) approaches another rat sideways or broadside ("crab walks"), with his back strongly arched, and crowds the second rat. Sidling may a successful strategy to counter boxing and acheive a rump bite. If physical contact is made, the sidle may become a push. The sidling rat may also kick.

Sleep: Periodic suspension of consciousness.

Sniff: cluster of movement sequences in which (1) the rat probes its snout along and around surfaces in a series of discrete head movements, (2) the tip of the snout and the whiskers are in brisk motion, (3) the rat breathes in and out rapidly (Welker 1964). Sniffing is often a component of exploratory behavior. Through sniffing, the rats sample their surroundings by smell and whisker-touch.

Solicitation: Female initiation of sexual interaction. A female rat in behavioral estrus will attempt to initiate and maintain mounting behavior by soliciting the male. She darts towards him, then runs or hops a short distance away. She may wait a bit, move back, wiggle her ears, and repeat the sequence. This is called full solicitation. In partial solicitation she pauses in front of the male (touchback) or runs past him (runby). In an interception, she darts in front of a male who is following another female and distracts him.

The male rat finds these behaviors very attractive, and he may be motivated to follow and mount the female. The touch on her back triggers lordosis in her, the female arched-back mating posture that enables copulation. For more, see Nelson 1995.

Squeak, long: Loud, high pitched 0.2-0.3 sec note that stays relatively constant in pitch. Given by subordinate rat during belly-grooming, during other tense encounters, or in strong protest. A variation is the broken long squeak, which is a long squeak that is broken into two notes. To read more about long squeaks and to hear squeak samples, go to the Norway Rat Vocalizations Page.

Squeak, short: High pitched, 0.2 sec note that sweeps slightly upwards in pitch. Heard during head grooming and mild social interactions. Variations include the chirrup (broken, double-note short squeak), and the squeak-churr (sqeak that ends in a broad-band vocalization that sounds like a soft "churr"). To read more about short squeaks and their variants, and to hear squeak samples, go to the Norway Rat Vocalizations Page.

Tail carry: rats may pick up their tails in their mouths and carry them. May be a form of displaced maternal behavior by mother rats. Pregnant rats who are deprived of all nesting material still attempt to build nests by carrying their tails again and again to the chosen nest site. Mother rats with nursing litters may retrieve their own tails to the nest.

Tail writhe (tail wag, tail swish): Tail moves sinuously on the ground, and may bang on the floor. The movement may involve the entire tail, or as little as the tail tip. Tail writhing is frequently seen during nose-offs. I have also been able to elicit tail writhing by covering the rat's head with my cupped hand and pressing down gently.

The function of tail writhing is unknown. Tail writhing may indicate a high degree of tension or excitement, possibly negative excitement. For example, lactating females may swish their tails during aggressive encounters with each other (Adams and Boice 1983).

Tonic Immobility (also: cataleptic immobility, paroxysmal inhibition): Freezing behavior seen when pressure is applied to the upper back/nape of a rat (Grant and Mackintosh, 1963; Lehman and Adams 1977; Meyer 1990; Tikal 1991; Webster et al. 1981).

Tonic immobility may be seen when a rat performs a belly-up roll during an agonistic encounter. In this position, when the rat is completely prone, his upper back may contact the floor and the pressure may trigger a tonic immobility response which keeps the rat immoble for some time. Tonic immobility tends to last longer in subordinate rats (Tikal 1991). Tonic immobility may also serve to reduce the probability of an attack during a conflict, as animals prefer to attack moving targets (Thor et al. 1981). Immobility will not, however, inhibit all attacks as Blanchard et al. (1977) has shown that a motivated resident rat will attack an anesthetized intruder.

Tonic immobility can be artificially triggered by humans who apply pressure to the upper back. Tonic immobility may be related to dorsal immobility, in which a rat freezes when picked up by the scruff.

Tonic immobility may be related to "playing dead" or "animal hypnosis" in other species (e.g. guinea pigs, rabbits, chickens, quail etc.). For example, chickens who are manually restrained by a human may go limp and stay that way for some time.

Trot: Gait in which legs within the girdles step in alternation (the two front legs alternate between themselves, and the two back legs alternate between themselves), and diagonal pairs of legs move in synchrony (front left and back right move together). This gait is intermediate in speed between the walk and the gallop.

Urine mark, or scent mark: The rat deposits tiny droplets of urine on the surfaces and objects he walks on. Considered an advertisement of the rat's presence and a sex attractant. Urine may be deposited by: (1) anogenital drag: rubbing hindquarters over top of object, leaving a trail of urine as the rat steps over it; or (2) leg-lift: lifting hind leg nearest the object and urinating on one corner while standing, or walking beside the object with one hind foot on top of it, leaving a trail of urine along the entire length of the object (Brown 1975). Rats may urine mark each other using the (3) crawl-over. Visit the urine marking in Norway rats page for more.

Ultrasonic vocalizations (USVs): Vocalization above 20 kHz. Rats emit different USVs in a variety of contexts. Different types of ultrasonic vocalizations include:

* Infant distress calls: Infant rats, who cannot regulate their own body temperature, emit high pitched, 40 kHz distress calls when they are cold (Allin and Banks 1971; Carden and Hofer 1992).

* Long distress USVs: Rats emit long 20 kHz vocalizations when they are unhappy or stressed. For example, these calls are emitted when an adult or juvenile is defeated socially (Thomas 1983), sees a predator (Blanchard 1991), experiences pain (Cuomo 1988, Tonue 1986) or anticipation of pain (Antoniadis 1999).

* Short, chirping USVs: these calls are shorter and higher pitched (50 kHz) than the negative SVUs (Knutson 1999), and are thought to be positive. Adults and juveniles emit them during play (Knutson 1998), courtship (Barfield 1979), and in anticipation of feeding (Burgdorf 2000). Here's an article on "laughing in rats" as well as a summary article written by the researchers.

For more, see What do Rats Hear?

Walk: Lateral sequence gait, with no period of free-flight (all four legs off the ground). Walking is the slowest of rat gaits.

Yawn: Deep intake of breath through wide open mouth. Frequently associated with stretching. For some wonderful photos of rat yawns, check out the Dapper Rat Gallery of Yawns page.

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