Plot hole: Even if the white blood cells will attack and destroy the sub and the body of Doctor Martin the atoms would still remain and take normal size after the critical 1 hour is up. This would also apply to the laser gun which they forgot or left behind on purpose, as well as several dozen litres of saline solution which were miniaturised and pumped into Benes' body. He's in a lot of trouble.
Revealing mistake: Near the end of the film when a building is collapsing and people are running to escape the falling debris, several women along with James Coburn are running up some stairs; a block of cement falls and hits actress Gina Golan right in the head. Instead of killing her on the spot, the bolder merely bounces off her head and she continues running up the stairs. (01:40:55)Mark Pitta 1
Revealing mistake: Near the beginning, Montag puts on the fireproof clothing to use the flamethrower. It's really footage of him later taking off the same equipment played in reverse.
Continuity mistake: When Wyler and Susan are escaping in the van, the windscreen is shattered and Wyler punches a hole for visibility. In all further shots of the van, the windscreen is obviously intact with the shattering merely cosmetic.