It's supposed to be a kind of Tear Jerker moment, with some sympathy for the villains, but the way Cairo freaks out after they find out the bird is a fake can make you laugh.
Cairo: You... you bungled it. You and your stupid attempt to buy it! Kemedov found out how valuable it was— no wonder we had such an easy time stealing it! You... you imbecile!You bloated idiot! You stupid fat-head, you—[He then proceeds to cry like a little baby]
Poor Joel Cairo's the Butt Monkey of the whole movie. There are those who think the title should go to Wilmer, but let's be honest, Cairo got slapped around lots more than Wilmer. It kind of helps that Cairo is kind of charismatic, likable and charming, where Wilmer's just a bit of a sullen hot-headed jerk.
Joel Cairo: I certainly wish you would have invented a more reasonable story. I felt distinctly like an idiot repeating it.
Sam Spade: Don't worry about the story's goofiness. A sensible one would have had us all in the cooler.
Dude! He even got bitten once!
The scene where Cairo attempts to search Spade and his office at gunpoint, but Spade manages to disarm him and talk him down. Once they're done, you think Spade's persuaded Cairo to back down a bit, so Spade gives him back his gun — and Cairo immediately holds him at gunpoint and demands to search the office again. Even Spade bursts out laughing.
Spade:[Amused] Alright, buddy, I ain't gonna stop you.
Spade relieving Wilmer of his handguns is awesome. His explanation afterwards to Gutman, meanwhile:
Spade: You shouldn't let him go around with these on him, he might get himself hurt.
Gutman: Well, well, what's this?
Spade: A crippled newsie took 'em away from him. I made him give 'em back.
And, later on:
Spade: I hope you're not letting yourself be influenced by the guns these pocket-edition desperadoes are waving around, because I've practiced taking guns from these boys before, so we'll have no trouble there.
Spade goes before the district attorney, who thinks he's concealing evidence about who killed Thursby. This, and the fact the police suspect him, does not go over well with Spade, and he starts chewing out the district attorney. Mid-rant, he turns to the stenographer:
Spade: You getting this all right, son, or am I goin' too fast for ya?
Stenographer: No, sir, I'm getting it all right.
Spade: Good work.
There's something sort of funny about Cairo asking Sam to "please" put his hands over his head so that Cairo can search the office, as if he doesn't realize that he doesn't have to say "please" while he's got a gun pointed at Sam.
And after Spade relieves him of his gun and hands it back, Cairo points the gun at Spade again and tries to interrogate him while continuing to be polite! Spade's reaction pretty much screams "You Have Got to Be Kidding Me!"