Ace High hands...

[Nietzsche]

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On the river, its pretty tough to get a feel for which guys will fire two bullets and which guys will give up when you call the turn

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Yeah, this is also one of those spots where passives sometimes change character as it is a very bluff friendly situation. And if he decides to bluff on the turn he will almost always fire on the river also, as opposed to some more aggressive opponents who figure if you call the turn, you are very likely to go to showdown so they give up on the river.