By themselves, each of these behaviors can just be signs of stress, or even a person's natural mannerisms. One can occur by chance, but when two or more of these behaviors suddenly appear at a moment when lying could be expedient, you should be skeptical. For example, when you ask a salesman how reliable that used car is, it suggests he's lying.

Here's the top eight list of suspicious behaviors:

1. A change in the voice's pitch.
2. A change in the rate of speech.
3. A sudden increase in the number of "ums" and "ahs."
4. A change in eye contact. Normally, one makes eye contact one-quarter to one-half of the time. If suddenly, at the convenient moment to lie, he's staring at you or looking away, beware.
5. Turning his body away from you, even if just slightly.
6. Suddenly being able to see the white on the top and bottom of a person's eyes, not just the sides.
7. A hand reaching, even if momentarily, to cover part of the face, especially the mouth.
8. Nervous movement of feet or legs.