Goofs

In one scene in the film, the panicked crowd fleeing from Reptilicus runs to the left and down an alley. Later, they run to the right down the same alley.

At 15:42 into the film, the "freezing room" door's lock latch is cast metal and painted white. When the door is seen again at 15:56 into it, the latch has become smaller with a chrome finish.

In the film, the female scientist says they would need at least a gallon of the drug to knock out Reptilicus. She uses a 2 liter beaker to fill the shell. That is little more than half a gallon.

Since many different marionettes were used to portray Reptilicus in the film, his appearance often kept changing from scene to scene. Sometimes the frills on his neck would be doubled or his random tufts of hair would go from the top of his body to the bottom of it.

In one scene of the film, blood is gushing from Reptilicus' mouth even before the drugged missile is shot into it. Then in the next scene, the blood is suddenly gone.

Acid does not set buildings on fire.

At 37:00 into the film, during the briefing General Grayson calls a naval officer "Commander Svendsen" and he nods agreement. Svendsen is wearing the four sleeve stripes of a captain.

In the film, when Dr. Dalby goes into the "freezing room" to take a sample from the frozen section of Reptilicus' tail, its flesh is very soft and is nowhere near frozen.

Throughout the entire film, Reptilicus repeatedly changes scale compared to buildings and people.

When General Grayson rides in a tank in the countryside and shoots a flamethrower at Reptilicus, a camera is clearly mounted on the front of the tank (for the low-angle closeup shots of Grayson firing the flamethrower).

Toward the end of the film, before Grayson fires the rocket launcher containing the drugged missile, the launcher is clearly not loaded in one scene of it.

In a handful of scenes in the film of the crowds fleeing from Reptilicus, some people are obviously smiling or have comical expressions on their faces. During the scene on the bridge, many people are just calmly standing around.

The film begins in the frozen mountains of Lapland, above the Arctic Circle. However, there is no snow shown in the first scene, and the miners appear to be in a tropical jungle instead.

Denmark is not a part of Lapland, a region of Eurasia that includes northern Norway, Sweden, Finland and Russia. The Norwegian part of the region is sometimes called "Danish Lapland," which might have confused the filmmakers.

The scientists supposedly got from Copenhagen to Lapland in two hours. It would take at least six hours now, and probably more back then.

Despite Brandt's insistence that the drugged missile will only work if it is fired point-blank into Reptilicus' mouth, Grayson shoots it from the other side of the city square and easily hits the target.

Captain Brandt informs General Grayson that, in order to shoot the drugged missile into Reptilicus' mouth, he will have to fire point-blank. He then adds "at very close range." He basically says the same thing twice for no reason at all. Grayson, an experienced army general, would have known what "point-blank" meant.