Raiders of the Lost Ark (1981)

Revealing mistake: While Indy and Marion are in the Well of Souls, and they encounter the snakes, Indy falls to the ground only to be confronted by a hissing Cobra rearing its head. Look carefully and you'll see the snake's reflection on the safety glass between it and Indy. Briefly you can also see the torch's reflection while he's waving it around. You can also see Marion's reflection when she falls in later on and is face to face with the cobra. [This has been corrected in the new DVD set. You can only see it if you have the original VHS. I think it's visible in the "making of" on the DVD as well.]

Indy: There's a big snake in the plane!
Jack: Oh, that's just my pet snake Reggie.
Indy: I hate snakes, Jack! I HATE 'EM!
Jack: Oh, come on! Show a little backbone, will ya?

Trivia: When a Nazi falls from the back of the truck carrying the Ark, a "Wilhelm scream" can be heard.

Question: After the scene where Indy first goes onto the German U-boat, he runs around apparently looking for something, then the scene changes to the inside of the sub where you can hear that the order has been given to dive. Was there an actual scene cut out of the film where Indy lashes himself to the periscope? (When Raiders first came out in Aus, I vividly remember seeing it with this scene.)