See Shrub lie

What are the clues that tip you off that you're watching a lying liar in action?

From the FBI Law Enforcement Bulletin June 2003 Issue:

...A person’s level of comfort or discomfort is one of the most important clues interviewers should focus on when trying to establish veracity. Tension and distress most often manifest upon guilty people who must carry the knowledge of their crimes with them. Attempting to disguise their guilt places a distressing cognitive load on them as they struggle to fabricate answers to what otherwise would be simple questions....

...Interviewees often will show their displeasure by rolling their eyes out of disrespect; picking lint off themselves (preening); talking down to the interviewer; giving short answers; becoming resistant, hostile, or sarcastic...

...Research also has shown that when people are nervous or troubled, their blink rate increases, a phenomenon often seen with liars under stress. In one case where investigators closely videotaped the interviewee, observers in another room catalogued the subject’s blink rate increase from 27 times per minute to 84 times a minute during stressful questions.

Dembloggers has the video evidence. Judge for yourself.

And just for fun take this test to see if you can Spot the Fake Smile. Years of practice reading kids' faces got me 15 out of 20 correct.