Why does my cat suddenly change and bite me when I'm stroking it?
Sometimes, when cats are the centre of attention, they will change because they suddenly feel threatened by the person who is cuddling them. This behaviour can happen in most cats, but what varies is the point at which they change from being affectionate to being aggressive. It is sometimes called the 'Petting and Biting Syndrome'.
One explanation is that the individual cat's past affects the tolerance levels for feeling trapped. A cat that has been handled from an early age and is used to being petted will have a high threshold, and will rarely show aggression. Those that have been handled less will show an aggressive reaction within a few minutes of being picked up. It may also be that past unpleasant experiences are associated by the cat with being held.
Another explanation is due to cats' grooming behaviour. Mother cats spend a fair amount of time grooming their kittens and the human hand may well be thought of as an equivalent to the mother's tongue. At first, when being stroked, cats are comforted by this 'maternal grooming' and relax, but suddenly there comes a point where they are adults once more. The human hand is now the dangerous paw of another cat, and has to be fought off.
Treatment for this syndrome takes time. The 'threshold' of the reaction time has to be increased. The cat should be fussed in very short sessions, without even picking it up. Once it is OK with this, put the cat onto your lap, stroking the back and neck but avoiding sensitive areas such as the abdomen and legs. Gradually increase the amount of time spent petting, but never restrain forcibly as this will only lower the tolerance threshold and undo everything!