Training & Behavior

Eight o'clock on a Tuesday. Both cats are on the windowsill doing their evening surveillance. A tomcat you have never seen strolls along the top of the fence. Your tabby's tail goes up like a bottle brush, she makes a noise you have never heard out of her before, and then, because the fence is on the far side of a pane of glass and the tomcat is completely unreachable, she spins round and lands on her sister. Fur, screaming, a smear of blood on the radiator. Twenty seconds later it is over and you are standing in the doorway with a tea towel, wondering what just happened to two cats who were curled up together that afternoon.

This is redirected aggression, and it is one of the most misread things cats do. The arousal has nowhere to go. The threat is behind glass, the adrenaline is already up, and the nearest available body takes it. The other classic version is cats fighting after vet visit day, where one cat comes home smelling of clinic and antiseptic and gets set upon at the door by a housemate who has lived with her for six years.

The part that catches owners out is that the fight does not end when the trigger leaves. The tomcat wanders off, the window is empty, and the two cats still hate each other a week later. That is because the fight itself is now the problem. Your second cat is genuinely frightened of the first one and starts moving like a frightened animal, crouching, staring, bolting out of rooms. Your first cat is still flooded with adrenaline for a day or more and reads all of that as a reason to go again. Every subsequent encounter teaches both of them the same lesson. Cats are also not built for reconciliation the way dogs and primates are. Their strategy is avoidance, and you have just put avoidance out of reach by keeping them in the same flat.

So the first job is separation, and it needs to be total. Not a baby gate, not supervised time in the kitchen. Two rooms with the doors shut, each with its own litter tray, water, food, bed and somewhere dark to hide. Keep it quiet and boring for at least twenty-four to forty-eight hours, because that is roughly how long it takes for stress hormones to come down, and in some cats it is longer. Trying to reintroduce them on day one because you feel guilty is the most common way this gets dragged out into a three-month saga.

Whoever told you to let them sort it out was wrong, and the advice does real damage. Cats do not fight until a winner emerges. They rehearse. Each fight makes the next one more likely, faster and more serious, and somewhere in there one of them starts urinating outside the tray because a predator now stands between her and it.

How you break up a live fight matters. Do not reach in, do not grab a collar, and do not scruff anyone, because you will be bitten and cat bites land people in hospital. Put something between them, a cushion, a laundry basket, a piece of cardboard, or make a loud noise from another room and let them scatter. Never throw water and never shout afterwards. You will only add yourself to the list of frightening things in the house.

Get both cats seen. Puncture wounds hide under fur and turn into abscesses three to five days later. More importantly, ask your vet to look at the aggressor properly, including bloods if she is middle-aged or older. Arthritis, dental disease, hyperthyroidism and hypertension all lower the threshold for lashing out, and a genuinely painful cat cannot be trained out of it.

Then remove the trigger, or none of the rest works. Frosted window film across the bottom metre of the glass is cheap and it fixes this in an afternoon. Move the cat tree away from that window. Close those curtains at dusk. Outside, stop feeding neighbourhood cats near your house, block the gaps under the fence, and consider a motion-activated sprinkler on the route the tomcat uses. If your cat can still watch him patrolling, she is topping herself back up every evening.

The reintroduction runs on scent first. Swap bedding between rooms, rub a soft cloth on one cat's cheeks and leave it where the other one can investigate it, rotate which cat has the run of the house so each gets used to the other's smell without a face attached to it. Next, feed them either side of the closed door, bowls far enough back that both eat calmly, and move them closer by a few centimetres a day. Only when both are eating relaxed do you go visual, through a mesh screen or a door wedged open a couple of centimetres. Thirty seconds, food, done. Any hard stare, any hiss, and you shorten the distance and try again tomorrow.

Supervised sessions come last, kept short and ended while both cats are still bored. Set the house up so neither has to compete. Litter trays should number one per cat plus a spare, in separate places, with food, water and beds spread out and plenty of high shelves so one cat can move up and past instead of squeezing by.

A pheromone diffuser is a reasonable adjunct and not a solution, so run one but do not expect it to carry the plan. For a badly affected pair, your vet may discuss short-term medication alongside the behaviour work, and if there has been serious injury or the fear is not budging, get a qualified force-free behaviourist involved rather than improvising.

Realistically this takes two to eight weeks, sometimes longer, and progress is not a straight line. Most pairs do come back to something close to what they had. A few end up as polite housemates who share a home and not a bed, and that is a perfectly decent outcome. What never works is speed.