Tells
In the field of poker, a tell is when you or someone else does something that reveals to other players that you are holding, or that you are not. Let us look at a school book example: In the movie “Rounders” rough poker player Teddy KGB (played by John Malkovich) often cracks open a cookie and listens to the sound of it. His opponent – our protagonist – Mike (played by Matt Damon) realizes that he only eats the cookie if he actually has something. Otherwise he just keeps it. When he notices this tell, he uses the knowledge for one round before informing Teddy KGB that he knows his tell. This might seem unstrategic to some, but it puts Teddy KGB off so much that the effect is even better than if Mike had just used the exposing to his advantage.
So a tell is when a player, unknowingly, gives a clue to his hand. It is not impossible that a tell is being faked, in order to fool other players, but if you watch someone for a longer period than you will probably be able to tell the difference.
There are many types of tells; whether you lean back or forward in the chair, the way you place your chips, your facial expressions, your tone of voice, the way you breathe, whether you fidget in some way or if you do something special with your drink, cards or cigarette. In other words, it takes good concentration and awareness to notice relevant differences in all of these different areas. It is not only the expression on ones face that is included in a poker face.
Also be attentive to things like if someone is trying to bluff and seem overly cocky by throwing the chips in the pot with confidence, or if they are blushing while they seem to speak in a very casual, almost bored way. Is the other player looking at his hand often, or does he/she seem overly calm? More than often, this is signs of acting the opposite way that he/she really wants to, in order to mislead the other players. So if someone seems aggressive or loud, than it is very possible that he/she really has nothing, but try to act like this wasn’t the case.