Walter Huston's cameo

I didn't readily pick up on the fact that that was Walter Huston (the director's father) playing the part of the mortally wounded ship captain that stumbled into Spade's office.

I do like this little bit from the Trivia section, though:

[Director] John Huston recruited Mary Astor to play a prank on his father, Walter Huston, after the elder Huston had filmed his cameo. Astor called up Walter, telling him she was producer Hal B. Wallis' secretary, and that Wallis thought he'd over-acted during his scene. Huston was enraged, declaring that he'd never been accused of over-acting in his life, but agreed to return the next day to re-shoot the scene. John then took the phone from Astor, identified himself as Wallis, and repeated the criticism. Walter grew even more furious, declaring that he'd already agreed to the re-shoot, and it was only when John exploded in laughter on the other end of the phone that Walter realized his son was playing a prank on him.