The Lost World (1960)

Revealing mistake: Whenever the dinosaurs are seen walking on dirt or sand, if you look closely, you can see individual grains of sand and small clumps of dirt. This would not be possible, unless the "dinosaur" was a foot and a half long at the most.

Challenger: Ah, Professor George H. Challenger and his lost world! Have you got your camera, Malone? I think a photo is in order.
Malone: You're quite right, Professor.
[Snaps a picture of Jennifer Holmes.]
Challenger: Reporters!

Trivia: Thanks to the money guzzling Cleopatra, the film company that put it out was forced to cut back their budget for other films like this one. Irwin Allen (director of this B grade epic) was forced to use real reptiles as dinosaurs instead of stop motion.