pinching and biting

I have a four year old son with autism who has started biting and pinching again. Sometimes he does it as a way of communicating when he wants something like a drink as he doesn't talk but mostly does it for no reason.

Does anyone have any tips or advice on how I can get him to stop? It doesn't happen all the time but all the same it's not a very pleasent expirencefor all involved.

Many thanks x