When the Creature goes into the Lobster House restaurant looking for Helen, there is a clock on the wall over his head. When he leaves moments later carrying her, the clock has moved forward more than 2 hours.
In the scene where the Creature attacks a pair of college students, it picks one of them up and tosses him into a nearby palm tree. The line attached to the stunt double is clearly visible as he hurtles through the air.
When Professor Ferguson is informed of the capture of the creature, his colleague refers to it as a "creature from the Devonian era" and something that should have "...died out a quarter of a million years ago."
The Devonian is a geologic period, not an era (which marked the emergence and divergence of fish species and land plants, and, near its end, the first animals to venture onto land), and lasted from 416 million years ago to the beginning of the Carboniferous Period, 359 million years ago. As with the first Creature movie, the "scientists" not only do not know the terminology of geologic history, but their chronology is all wrong.
Early in the movie, when the men on the RITA II are shooting at the Creature, one of the projectiles meant to simulate bullets streaking through the water can clearly be seen bouncing off the Creature's back.
When the Creature drags Joe over the side of the holding tank into the water, two men jump in to save him. The Creature drags both of them under the water. When Joe jumps back in to save them, he only drags one to safety, apparently leaving the other one to drown.