[BruceZ]

The reason that happens isn't because they are bipolar or antisocial, but because they are misinterpreted as wanting a tummy rub, when in fact they are assuming a vulnerable position understood in the cat world to be a demonstration of submission and trust. With that in mind, you can understand why violation of that trust by tickling them at that moment is the worst thing that you could do, especially since many cats are especially sensitive on their tummys. They will respond this way every time, but if you just place your hand gently on its tummy without rubbing, he may just pause and then lick your hand instead of trying to bite it off.