When Hector is mixing up the gunpowder, he puts it in a tin can, not too common in prehistoric times.
During opening credits, the Earth is shown spinning backwards.
The cave women wear mascara and eye-liner.
Hector Servadac points to a prehistoric creature and says that the plantasaur has not been seen on earth for 1000 centuries. In addition to the plantasaur being a made up creature, 1000 centuries is only 100,000 years. The dinosaurs have been extinct for 66 million years or 660,000 centuries ago.
During the comet's approach, the string it is suspended upon is visible.
Some of the archive monster footage edited from One Million B.C. (1940), was shot in an anamorphic wide screen process, and is here seen squeezed to fit the narrower 1.85:1 non-anamorphic ratio.
When the group goes to higher ground to battle the lizards, a caveman lightly kicks the heavy boulder, which easily moves.
Once again, an Italian actor is playing a Frenchman, as seen more recently on The Nanny. However, this one playing Hector Servadac talks with more of a vague Anglo-British accent and doesn't even attempt the silly caricature French accent that Americans are so notorious for.