This is similar to the "I'll bet I Can Wait Longer" tell. However, in that tell, the player had her arms folded, which implies that generally she's in long-range waiting mode. Some players lean slightly forward when they're interested in a hand and otherwise (as in this video sequence) slump slightly backward. Players may even be aware that they're doing this, but it's too much effort for them to try to camouflage their behavior -- especially when they figure nobody is watching for it.
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If you act before this player, play some slightly weaker hands which you would normally pass. That's because this player is no threat to you at the moment. She's making it easier for you to steal the antes.
