DS tends to bite things when he gets frustrated. The blocks won't stack right - he bites a block. The towel won't fit all the way into the cup - he bites the towel. Usually with a grimace and grunt, sometimes followed by crying. When there isn't any object to be angry at he bites his own hand. (These are situations like really wanting to get out of his car seat while we're driving or not being allowed to have the knife he was reaching for.) He often leaves teeth marks, but never draws blood and doesn't act hurt afterwards. Just one bite for a second or two and then he's done. I firmly tell him "no bite" but often that seems to frustrate him more because I'm reprimanding him in the middle of an already frustrating situation. This isn't the *only* way he responds to frustration, just sometimes. Maybe once a day.
So my question is: how normal is this? Should I be concerned? Is there something I could/should do differently? Or will it pass on its own?