Goofs

Mike wires the explosives to the detonator box and the plunger is all the way up as he walks over to Steve and the rest of the group. Steve then walks over to the detonator box to set off the charge but now the plunger is down, he has to pull up before he pushes it down to set off explosives.

Doc Greyson uses the incorrect plural term for the octopus, "octopi." The correct plural of octopus is "octopuses" or "octopodes."

Correction: Although some scholars believe that "octopi" is an incorrect assumption about being the correct plural form, it is generally agreed upon that "octopuses" sounds wrong to most users and "octopodes" is largely unknown. That makes this not a character error.

The film's promotional poster shows two women trapped in the den of the giant leeches. The woman in the poster dressed in red was never in the movie.

Cal and Dave are talking outside the general store. The reflection of the mike boom can be seen in the roof of the car.

When Steve and Mike are preparing to go underwater, Mike calls Steve "Mike."