It is one of the most bewildering things cats do: settle into a lap, enjoy a few minutes of fuss, then whip round and bite the hand doing the fussing. It looks like betrayal and it is nothing of the kind.
It is usually too much of a good thing
Many cats have a fairly low ceiling for being stroked, and once it is passed the sensation tips from pleasant to irritating. The bite is not an ambush; it is the cat's blunt way of switching off a session that went on past its comfort, after quieter requests to stop went unread. Behaviourists call it overstimulation, and the cat that does it is not a mean one, just a specific one.
The warning it gives first
The bite almost always has a preamble. A tail that starts flicking or thrashing, a ripple running along the skin of the back, ears that swivel back or flatten, a body that tenses, a purr that stops, or a head that turns pointedly toward your hand — any of these is the cat saying enough. Learn to end the stroke at the first of them and the bite mostly disappears, because you are answering the question before it has to be shouted.
Working with the limit
Keep sessions short and let the cat start and finish them. Favour the spots most cats genuinely like — cheeks, chin, the base of the ears — over the belly and the base of the tail, which many merely tolerate. Reward the calm and never punish the bite, which only teaches the cat that hands are unpredictable. One caveat worth keeping: a cat that suddenly starts biting when touched where it never minded before may be in pain, and that is a reason to see the vet rather than to read body language.
Why does my cat bite me when I am petting it?
Usually overstimulation — the cat has had more stroking than it finds comfortable and bites to end it, after subtler signals were missed. It is not spite, and reading the early warning signs largely prevents it.
What are the warning signs before a cat bites?
A flicking or thrashing tail, skin rippling along the back, ears turning back or flattening, the body tensing, a purr stopping, or the head turning toward your hand. Stopping the stroke at the first sign usually heads off the bite.
Should I be worried if the biting is new?
Possibly. A cat that suddenly objects to being touched where it never used to may be in pain, so a new onset of biting is worth a vet check rather than a behavioural fix alone.