For the past 6 weeks or so, or 9-month-old son has been in the habit of sticking a finger far into his mouth; to the point where he coughs; and sometimes throws up as a result.

If we are next to him when he does it, we physically remove his hand from his mouth. We have also tried lightly tapping/slapping his hand when he does it, and telling him "No" firmly.

Related information; he has 2 teeth that have come pretty far in; no others yet. He eats very well and eats a lot.

Is this a common occurrence; and what techniques can we use to help prevent it from happening? The primary goal is to stop him from choking or throwing up.