Surprising a dog from behind, forcing him into a corner, waving hands in the air or screaming may overexcite him, causing him to snap in fear or even in play. Let a dog eat in peace. If there's one place a dog may get defensive, it's at the food dish. Your dog shouldn't growl when you get near his dish, but you shouldn't interfere with his eating. Watch out for special toys.
Some dogs have powerful feelings for their balls or chew toys.
Never take a bone or toy from a dog's mouth unless you have trained him to drop it and give it to you first. Dogs may get too enthusiastic in these sorts of games and forget you're not a dog. Fetch, Frisbee, hide and seek, agility courses, and flyball are better outlets for your dog's energy. Respect a dog's space. Dogs naturally defend their territories.