The player feels he has the winning hand and wants to make his opponent's bet seem safe.
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It's the last part of the sequence that you should concentrate on now. In any type of poker, players who act like they're going to discard their hands or rap pat before the action reaches them should be considered a threat. There's no reason for them to use these maneuvers unless they're trying to fool you. This is definitely a tell where the player is trying to act weak because he is strong. Here, he has a double motive. Not only is he telling his opponent at left that the bet is safe, he's encouraging the other opponent (who must act next) to call.
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Abandon all bets! Even if you have a very strong hand, it's usually better to let the player with the straight bet for you. You can later raise with your full house. Don't bluff and don't expect to catch the player in the foreground bluffing. Not this time.