
Some players, when holding a weak hand, will tend to stare at the board after betting.
Many players find the board the safest place to look after making a bluff.
This tell is not a strong indication if you haven’t correlated it with a specific player’s behavior; some players (including many good players) will stare at the board after betting no matter if they are strong or weak. This is why the post-bet tell is less reliable than the similar waiting-for-action tell. In other words, waiting-for-action staring at the board is more indicative of weakness than is post-bet staring at the board.
As with the pre-action tell, you will sometimes see bluffers adopt a quizzical expression after betting, as if finding something very interesting in the middle of the table. This is typically just another sign of weakness.
THREATENING TO FLIP A HAND OVER
A player who acts as if he’s going to flip his cards over in response to a potential call is usually weak.
The threatening-to-turn-your-hand-over move is a pretty common closing-action tell (“closing action” means an action that will completely close the betting on the hand) seen at lower stakes. You can often see it happen very clearly when a guy bets, another guy goes to call, and the bettor, almost in a threatening manner, prepares to flip his cards over. It can sometimes appear like some comical Western stand-off, with the one guy getting ready to draw his gun (call) and the other guy reaching for his own gun (threatening to flip his cards).
This tell will usually manifest itself more subtly. Sometimes a bluffer, when faced with an impending call, will just barely pick the cards off the table, as if in the beginning stages of flipping the cards over.
These players think they’re about to get called, so what’s the one weapon they have left in their arsenal? They act like they’re ready to confidently show down a winner. It’s a last-ditch effort and you can’t really blame them. But if they really had a strong hand, would they be going out of their way to telegraph their confidence? No, probably not. This tell can sometimes be elicited by reaching for chips as if to call.

The player on the left has just put out a bluff bet. In an attempt to dissuade his opponent from calling, he holds his cards as if he’s ready to turn them over and go to showdown.
A visually similar, but opposite, tell.
There’s a similar-looking tell where a player, after betting, holds his cards up fairly high in front of him, almost as if he were showing them to someone seated behind him. This tell is indicative of a strong hand, not a bluff. It’s a relaxed behavior, whereas the threatening-to-turn-the-hand-over tell is more tense.