Brief, involuntary facial expressions that occur when people try to conceal an emotion.
They last only a fraction of a second (1/25 to 1/5 of a second).
Because they are controlled by the limbic system (emotional brain), they often leak out before the conscious brain can mask them.
Learning to spot them can help detect lies or hidden feelings.
Evolutionary
Micro-expressions
The truth flashes in 0.2 seconds