A: Dear "How can I make my baby stop biting?"
A normal phase of biting is very characteristic of babies, and generally will pass on its own. People do not like to be bitten, so their spontaneous look of annoyance certainly communicates the natural message--"Hey! Don't do that!" Trying to negotiate or discipline or correct the behavior of a baby this young is likely to backfire however. Your only goal is to try to distract your son or move out of reach or somehow shift the action so that it is about something else. You can say softly, "No no no. No biting people!" but your main goal is simply to change the channel.
A baby of 9 months certainly undersands a great deal of what other people say, I agree. But this does not mean that a baby of 9 months is really able to reason with you or change his behavior on the basis of your words. He is still so little that his impulses are pretty much in charge of his actions. If he feels like biting, he will do it. If may be that he is expressing in this manner some of his normal emotional aggression or fighting spirit. The fact that he smiles may reflect the ordinary pleasure that he takes in this aggressive activity. This is fine and perfectly normal. When he is old enough to argue with you, he will use clever biting words instead.
Elizabeth Berger MD
Child Psychiatrist and author of "Raising Kids with Character"