Back to writing about writing! But still riding the poker high …
If you’re a poker player it’s a thrill to see your favorite game up on the big screen—except when they get it maddeningly, mind-bogglingly wrong. Fair warning, James Bond fans, I’m going to beat up on Casino Royale a lot. As refreshing as it was to see Bond step in to the modern world by trading baccarat for hold ‘em, the film gets almost as much wrong as it gets right. But even Rounders, generally considered the best poker movie ever made, steps in it a few times. 
Here are some of the worst offenses:
All bets—call or raise—must be atomic actions.  If you put chips in the pot to raise, you can’t go back to your stack for a second helping. If you announce a call, you can’t subsequently announce a raise. That’s to prevent you from gleaning information from your opponent’s reaction and then modifying your action.
How many times have you heard some variation on this line of dialog: “I’ll see your twenty dollars … and raise you a hundred.” Here’s an example of a verbal string raise from Maverick. 
I understand why the line appeals to writers. It’s got drama! Suspense … and a reversal! But it’s a string bet, and it’s not allowed.
Table stakes are the default, meaning players are only allowed to bet what they have on the table in front of them. The shorter stack (in a heads up hand) is the effective stack, meaning that’s the most that can be won or lost in the hand. If you’ve got fewer chips than your opponent, you can’t bust them, no matter how good your hand. You’re not allowed to dig in your pocket for extra cash or a family heirloom to swell the pot.
In the first poker scene in Casino Royale, Bond’s opponent, who’s been losing steadily, tries to add his Aston-Martin to the pot when he thinks he holds the winning hand. To be fair, the dealer does object (saying “table stakes”), but then they go ahead and do it anyway. (How else is Bond supposed to win his car and steal his girl?) 
Conversely, if your opponent has fewer chips, you can’t push them out of the pot by overbetting. Unless you’re playing with some bizarre house rules, no one should ever be writing a check to fade a bet (as they do in this scene from Kaleidoscope).
A tell in poker is when you pick up on some unconscious tic or mannerism that alerts you to the strength of your opponent’s hand. This is legit, and entire books have been written on the subject,  but it’s almost always overdone on film. Take this scene from Rounders, where Teddy KGB’s tell is eating a goddamn Oreo. 
Granted, film is a visual medium with a compressed timeline, but that’s so blatant, so far beyond tensing your jaw or tapping your feet, that in real life, it’s far more likely to be a false tell—like a street hustler’s game of three-card monte, where you “discover” that the queen has a bent corner. Get ready to lose a lot of money, son.
That’s still better than Casino Royale, where the villain’s tell is that he bleeds from his eyes. (Seriously.) Partial credit for setting up exactly the kind of false tell I mentioned earlier in the final poker scene.
Skill versus luck
Poker is a skill game, but it’s also a luck game. In the long run, a disciplined pro can make consistent money. But in the short run? Anyone can win. Unfortunately Hollywood tends to get this exactly backwards, and their heroes win in the short run. And not by demonstrating any particular skill (other than reading an obvious tell) but by simply holding the right cards. How many times have you seen this scene:
Villain: “There’s only one hand that beats me.”
Hero: (has that hand)
Poker players complain about the insane clash of monster hands in the tournament finale of Casino Royale because it’s unrealistic, but there are bigger problems. The first is that Bond should never have been in the game in the first place. Thinking he can go in and win on skill is a terrible plan because luck is always a factor.  The second is that Bond’s victory is a pure gift from the screenwriters who dealt him a straight flush. Yeah, it’s cool to have the nuts, but that’s not a plan, man.
Next time: more poker sins, including the greatest sin of all
 There’s an argument to be made that Molly’s Game is a better poker film than Rounders, but this footnote is too small to contain it.
 Digging in the footnotes for some nuance? Here you go. The exception to the atomic betting rule is if you verbalize your action. If you say, “I raise,” then you can put out the call then add chips for the raise. If you say, “I raise ten thousand,” you can take as many trips as you like to get transfer all those chips across the betting line. Note: if you announce a raise, you must raise. That prevents shenanigans like, “I’m all in.” (Opponent calls.) “Just kidding.” Witness the controversy as a notable player attempts exactly this “joke” at the Bicycle Club in LA
 Casino Royale has three credited screenwriters. I suspect the scene was written as it plays, then a subsequent writer with more poker knowledge thought, “Ugh, no, we can’t do that … but it’s a plot point. Fuck it. Acknowledge it and move on.”
Personal anecdote: I’m not advanced enough to make this a big part of my game, but I have read the books, and trembling hands are supposed to be one of the stronger signals—the idea being that the player’s adrenaline is spiking because they’re about to crush you with a monster holding.
Midway through a tournament at the Venetian, I folded my overpair to the board when the gentleman to my right led out with a huge bet and I noticed his hand was shaking. I figured I had to be up against two pair or a set, but he showed his bluff. Trembling hands are hard to fake, but what I hadn’t noticed at first (he was new to the table) was that his hands always trembled, as if had mild Parkinson’s or something. Whoops.
 Did you catch that Teddy KGB also makes a string bet? He makes two motions getting his chips into the pot without a verbal declaration first.
 That’s also the plot of Kaleidoscope.