The biting reflex when rubbed on the tummy is an instinctive behaviour. In domesticated cats it is stronger in some individuals than others. Saying, "No!" when the cat bites in this situation will have no effect on it's behaviour.....a bit like the doctor saying, "No!" when he taps your knee and expecting you to learn not to move your leg. It is strongly linked to sexual behaviour and the cat will either have a strong urge to react when it is mature or it won't. Neutering has no effect on the behaviour. It's a cat thing!!!!