After the diving suit is discovered, Margaret Irving's character is seen in the background sneaking away screen right. In the next shot she has reappeared and sneaks away again.
When Captain Hook tries to stop the cops from using the hidden stairs @21:22 his 1911 pistol is cocked ready for firing. A moment later @21:42 the 1911 pistol is un-cocked (NOT ready to fire) without the captain manually de-cocking it as would be needed on that model of firearm.
When captain Hook has the cops at the hidden stairs and Detective Kelly tries to brandish his revolver it is twisted and corroded. When the two detectives are collecting the wallets a few minutes later BOTH Detectives have perfectly usable revolvers in their hands.
In many scenes, wires operating the octopus's tentacles can be seen. This was because real octopuses, although highly intelligent, resist the training necessary to perform stunts on cue, such as those required in this film.