Yes... my theory is that it’s an “aw, shucks, I would never lie!” smile when, in fact, we know that we have lied in the past, that we’re quite adept at lying, in fact, and the smile is a guilty smile, even if we’re telling the truth.

It’s a learned behavior — smiling is an attempt to defuse the accusation, I think, but also a sort of ‘you got me’ reaction.

We are liars because we have the primal sense of self-preservation. But we feel guilty about it because we’re taught that lying is wrong. Some people feel no guilt, of course. We call those people narcissists.