One of the biggest aspects of playing poker is to use any detectable change in a player's behavior as clues to assess the strength of his hand. These detectable changes in behavior are called 'tells'. Poker players attempt to correctly identify and interpret tells to gain an advantage. Often tells are subconscious and uncontrollable, and can very very reliable in nature. At a table full of professionals, however, just as often tells may be faked, in hopes that their opponent will make a poor decision in response to a fake tell.
Examples of Tells