Carl Showalter's part of a crazy criminal duo. He's an accident waiting to happen, He's a ticking time bomb.
Played by Steve Buscemi—in a role written expressly for him—Carl's a talkative, irritable, and fundamentally incompetent criminal. Carl thinks he's smart and sophisticated, but he makes some pretty ridiculous moves: committing the initial kidnapping in a moronic way, forgetting to put tags on his car, trying to bribe the state trooper who pulls him over, hiding the money-filled suitcase in a snow-covered field with a tiny windshield scraper to mark it… we could go on and on.
Carl's written as a small-time criminal who likes to impress prostitutes and act like a smart tough guy. He's in way over his head when he gets involved with someone like Gaear, who doesn't think twice about killing anyone in his way, including Carl. He's shaken up when Gaear shoots the state trooper—we get the impression that this really isn't his thing. In fact, when the trooper pulls him over, he says to Jean, covered up in the back seat:
CARL: Let's keep still back there, lady, or we're gonna have to, ya know, to shoot you.
At this point, it doesn't sound like he has any intention to shoot her. He pauses at "ya know" as if he's trying to make up something to say. Carl ends up killing two people in a rage anyway.
Human Powder Keg
Carl's a hothead. Here he is at his most typical, yelling at Gaear after Gaear wants to eat pancakes for lunch:
CARL: What are ya nuts? We had pancakes for breakfast. I want to go somewhere I can get a shot and a beer, and a steak, maybe. No more f***in' pancakes, c'mon man. C'mon man! Okay here's an idea. We'll stop outside of Brainerd. I know a place there we can get laid. What do ya think?
He also can't resist mixing it up with the parking lot attendant, who charges him for parking even though he went quickly in and out of the lot:
ATTENDANT: I'm sorry, sir, we do have to charge you the four dollars.
CARL: I just pulled in here. I just f***ing pulled in here!
ATTENDANT: Well, see, there's a minimum charge of four dollars. Long-term parking charges by the day.
CARL: I guess you think, ya know, you're an authority figure. With that stupid f***ing uniform. Huh, buddy?... King Clip-on Tie here. Big f***ing man.
Carl's temper has been building up since the murder of the trooper. His calls with Jerry just push him to the breaking point. When he finally sees that Wade has shown up with the ransom money instead of Jerry, he totally loses it. He has no idea how to deal with this unexpected turn of events.
CARL: Who the f*** are you? Who the f*** are you?
WADE: I got your goddamn money, you little punk. Now where's my daughter?
CARL: I am through f***ing around! Drop that f***ing briefcase!
WADE: Where's my daughter?
CARL: F*** you, man! Where's Jerry? I gave SIMPLE FUCKING INSTRUCTIONS –
WADE: Where's my damn daughter? No Jean, no money!
CARL: Drop that f***ing money!
WADE: No Jean, no money!
CARL: Is this a f***ing joke here? [He pulls out a gun and fires into Wade's gut.] Is this a f***ing joke?
Carl grabs the million dollars, tears out of the parking garage, and kills the attendant just for good measure. He really thinks this is all working out pretty well, except for the fact that Wade shot him in the face. He's still worked up when he gets back to the cabin, and he picks a fight with Gaear. We all know how that works out for him.
His volatile personality is his ultimate undoing. And by "undoing," we mean getting chipped up into itty-bitty pieces.
Carl even takes out his aggression on the TV at their lakefront hideout. (But honestly, can you blame him? That reception was terrible.)
Don't Think Twice. Or Once.
Carl is like Jerry in that he doesn't think things through. He's not acting like a guy who's trying to keep a low profile. When Jerry offers him the kidnapping job, Carl starts to entertain some logical doubts, like—why does Jerry need this money?—but he plunges in anyway.
After he and Gaear agree to the gig, they promptly start by leaving a trail of evidence, sleeping with prostitutes at a motel, hinting at their criminal history with a bartender, staging the kidnap in a ridiculous way, and then murdering three people including a state trooper.
When Carl finally gets his hands on Wade's money, he hides it in a totally idiotic way, burying it in the middle of snowy, featureless expanse, with a tiny windshield scraper to mark the place. The scene practically screams "There's no way he'll be back for this money."
Then, after returning to the hideout, he flips out at Gaear about how to split the value of the Ciera, prompting Gaear to kill him with an ax and dispose of his corpse in a wood chipper. Greed and a hot temper are what get Carl in the end. Even without the Ciera, Gaear would've probably killed him just for being noisy… like Jean.
Carl's a classic sociopath—no empathy at all. One of the most disturbing scenes in the movie is when the kidnappers bring Jean to the hideout and she tries, with a hood over her head, to run away. As she staggers around in confusion and terror, Gaear goes to get her and bring her inside, but Carl stops him.
He's getting a kick out of the scene and lets her stumble around a bit more while he watches and laughs. This is one of the few moments he feels in control; Jean's tied up and hooded and completely helpless. After he finds out Gaear killed Jean, he's too upset about his own injury and the money to care.