This player is trying to gain information about the advisability of a bet.
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If the player gets a threatening response, such as the grab-for-chips-and-stare threat used by the woman in the video clip, he'll go right ahead and bet, because the opponent probably has a weak hand. If instead of the threatening response he got a calm, non-threatening response, he would check and let the opponent bet, ponder his situation and then pass quietly without losing a single extra chip.
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If the rules of your game allow you to fake a bet without completing it, try this maneuver once in a while. Don't overdo it or your opponents will catch on.
