We've had our puppy for a few weeks, he is 16 weeks old. He's generally quite bitey which I know is normal and occasionally he'll bite us when he gets over excited playing or over tired. I'm not so concerned about this. He tries to chase cars and barks at them, so we have been trying to distract him with treats and eye contact, which sometimes works but sometimes he us so focused on the car or van that he will snap at us. Also if he is trying to chew something he shouldn't, or on furniture he shouldn't be and we try to stop him he will snap at our hands. Is this a cause for concern or normal puppy behaviour?