I'm among a few who have written about McCan't facial tics that give him away. In this post, I talk about his tongue jut which is an indication (likely) that he thinks he's getting away with telling a lie.
Well, here's a video of him today addressing an audience, asking, "Who is the real Barack Obama?" You can hear an immediate response of someone yelling, "Terrorist!" Just watch his facial expression. He is sort of taken aback by it, and his face sort of scrunches together before his eyes get very wide for just a second.
It sort of reminded me of the face he made after Joy Behar of The View challenged him that his ads were lies. Video here and below (about 6:30 in):
I'll let you decide, but I have my opinion (natch).