Obama is one of the best orators alive outside of acting. So it could be for effect, or it could be something more. He does take a long pause (not quite the 8 seconds as stated). During that pause, he does seem lost in his thoughts. Analyzing non-verbals is an art and a science, and there are subject matter experts out there. There are folks who have developed intuition from 10,000 hours of practice. Are there any current or former professional interrogators out there who can make something out of what seems to a layman to be an involuntary licking of the teeth as he's lost in thought? It's an odd behavior that I haven't seen in him before.