One of the most bizarre types of feline aggression occurs between cats when one cat is brought back from the veterinarian's office following some medical or surgical procedure. For some reason, the cat that remained at home may not to recognize his former buddy and may attack savagely. It can only be assumed that this is a case of mistaken identity and that the signals the returning cat put forth are somehow perceived as hostile or threatening. Who's Doing What to Whom?
The characters of the two cats are normally: Attacker – a dominant, willful, hyperactive, somewhat anti-social, unstable personality
Attacked cat – shy/fearful, introverted, anti-social, non-aggressive
The Cause of Sudden Change of Attitudes
One theory is that the cat returning from the vet's office smells different. Perhaps some chemicals employed by the veterinarian remind the incumbent of unpleasant experiences and set him on edge. For example, the residual odor of alcohol or disinfectants may rekindle memories of being forcibly restrained for injections. Another possibility is that a scaredy cat may have discharged her acrid smelling anal sacs at the vet's office. The secretions emitted are thought to contain an alarm pheromone, signaling danger.
Perhaps the behavior of the returning cat is different so as to confuse and alarm an overly sensitive yet controlling incumbent. People fear things that are strange or different so this theory is not difficult to swallow. If the returning cat looks different because he has been bathed, or because of stains on his coat, or if he stumbles out of the carrier like "Lurch" of the Adam's Family, the resident cat may panic and attack in self defense.
The Clinical Picture
The mode that the attacker cat adopts is sometimes that of feline affective defense behavior.
Piloerection – big bushy coat, tail hairs raised to produce a big puffy-looking tail
Pupils dilated – the iris of the eyes dilates fully so that the pupils become large black pools
Claws are unsheathed and ready for batting
Mouth opened threateningly
Hissing, spitting, growling
Ears pressed flat back against the head
The attacked cat may flee if he can, or may hunker down and try to make himself invisible.
Attacks may be savage and fur will often fly. Persons attempting to intervene may find themselves the subjects of the incumbent's aggression. Cats that are this wild will often redirect their aggression onto the nearest person or object.
What to Do
The first thing to do is to separate the two cats while simultaneously making sure that you do not become the target of the cat's aggression. Ideally the aggressor should be encouraged or herded into a separate room – such as a bathroom – giving him time, plenty of time, to settle down. Typically, a cat so enraged will take several hours to settle down. Even leaving the cat incarcerated overnight, with sufficient provisions and a litter tray, may not be overkill. The reintroduction of the two should only be attempted when the aggressor has completely settled down and is back to his old self. Even so, it should be accomplished tentatively and with escape routes planned. Reintroducing the two cats across a screen or via an inch crack in a door is a good plan so that the cats' attitude toward each other can be assessed before a full frontal introduction.
The chances that the cats' relationship or at least tolerance of each other can be reinstated are good, but future meltdowns are likely once this sensitivity has been recognized. In other words, history is likely to repeat itself if steps are not taken to prevent recurrence. Useful measures to take are as follows:
Make sure that a cat returning from the veterinarian's office is fully recovered from sedation or anesthesia before he is reintroduced to his colleague.
Insist on gentle handling of your cat at the veterinarian's office to minimize the risk of anal gland discharge.
Bathe the returning cat to remove veterinary-type odors before returning him to the household.
Keep cats separate for awhile after one returns from the vet's office until they re-familiarize with each other's sounds and odors.
It is almost impossible to prevent non-recognition aggression entirely. Whatever steps and measures you take there is always a chance that the behavior will be repeated. This is not to say that the measures to reduce the incidence are not worthwhile, just that there are no guarantees. The fundamental problem seems to involve the nature of the aggressor.
Content Provided By
This article was excerpted from the CD entitled "Behavior Problems in Cats - Etiology, Diagnostics and Treatments" by Dr. Nicholas Dodman, Professor of Clinical Sciences at Tufts University, School of Veterinary Medicine, © 1998, Trustees of Tufts College. To buy a full copy of the CD, contact