"Eye blocking" occurs when someone blinks for too long or covers their eyes.
Researchers have found that eye blink rate increases when you're under stress, like when you're nervous or when you're lying about something. It's an automatic physiological response, so you might not even realize when it's happening.
Hadnagy also cited pursed lips as an indicator of discomfort and, potentially, dishonesty. Some people may place a finger or a pen on their lips.
David Givens, an expert in nonverbal communication, writes in his book "Crime Signals" that President Clinton's lips "visibly pressed together, tightened, and rolled into a thin line each time he talked with reporters about the Lewinsky affair."
According to Givens, we instinctively tighten our lips to protect ourselves from danger — real or imagined.