
Some players bet with an aggravated expression after it has been checked in front of them. This often means a decent hand but not a strong hand.
I’ve seen this tell in lower stakes games, usually limit. It usually is in multi-way pots, when a number of players check to the guy who is last to act. The guy bets with a slightly perturbed, smirking look on his face, almost as if to say, “Well, if nobody else is going to bet, I guess it’s up to me.” Or it can happen in a heads-up pot where it’s been checked by both players on the flop and then checked once on the turn; the second player bets, but with that same expression of, “Guess I have to bet.”
As you would interpret from the classic “weak-means-strong” philosophy, this player appears upset with the turn of events, and so probably isn’t that upset. In my experience, though, he also won’t be very strong. Typically, when I see this tell, the player will have something like top pair with a medium kicker, or a second pair that he expects is good. It is hardly ever a very strong hand. A player with a strong hand in this spot would be more likely to remain stoic, or look disappointed as opposed to aggravated, in the hopes that someone gives him some action.
Interestingly, this is one of the few tells I’ve been able to regularly correlate with a medium-strength hand, as opposed to simply weak or strong.

On the flop, four players check to this man in late position and he bets. He has an aggravated expression, almost as if to say, “I guess it’s up to me to bet.” For most players, this will indicate a decent hand, but not a great hand.
BETTING IN THE DARK
Players who bet in the dark, before the next round of cards come, are more likely to be strong than weak.
An example of “betting in the dark” is when a pre-flop raiser gets called and then makes a bet in the dark, before the flop has come out. You see this more frequently in limit than in no-limit. With amateur players, this is almost always going to mean strength. It’s usually a hand like AA, KK, QQ, and maybe even AK, but not often much worse than that. The player holds a big hand and wants to get a little weird/creative/aggressive. When they’re holding a big hand is the best time to get a little creative, so they figure.
Sometimes there’s also an element of defensiveness, because they don’t want to be scared out of betting if the flop comes down real bad for them, so they make it easy for themselves and just bet in the dark.
Betting in the dark is sending a subtly passive-aggressive message; something like, “I don’t care what the other cards are, I can win this hand by playing you with these two cards right here.” Because people with weak hands don’t like to make aggressive statements (whether verbal or non-verbal), when a player bets dark, it is usually going to mean he started out strong. You could also group this hand under “strange behavior”, which is also usually going to mean strength from most average players. (See ‘Acting strangely’ for more information.)
A good player is capable of betting dark with a weaker hand, but I still would say a good player who does this is more likely to have a strong hand than a weak hand.
TREMBLING HANDS
A player who has trembling hands is often very strong.
The idea behind this one is: a player whose hands shake when he bets is showing a release of anxiety and/or a show of excitement. His cards are so strong that he is assured of a lock, and you are seeing his excitement and lack of fear. It will not be a bluff, because bluffers will be careful to hide their nervousness and will be still.
Mike Caro brought this tell into popular consciousness. People talk about this tell constantly as if it was one of the most important things he ever wrote, when it’s really just one of the more visually obvious tells that beginners have a good chance of spotting.
While this tell is generally true, I don’t think it’s useful for people to spend any time trying to spot this tell. I’ve only witnessed it a couple of times over the years, and it really is only of much use with players who are complete beginners. Only beginners will get so excited when they make the nuts that their hands will tremble—anyone with a small amount of poker experience just isn’t going to get that excited.
Also, you should be aware that there are many reasons people’s hands can shake. My hands can shake very slightly when my blood sugar is low. Old people’s hands shake for a myriad of reasons, like having Parkinson’s disease. Someone could be going through drug withdrawal. Just so you’re aware that this behavior can have multiple causes and is far from being an important tell.