Continuity mistake: When Johnny is walking out of the dirt bike stadium, he has his arms around two women's shoulders. The shot changes, now the two women are holding on to his arms. The shot changes again, and now his arms are free. It happens too fast for him to just let go of the women. (01:00:35)
Continuity mistake: When Mr. Fantastic is writing a problem on his chalkboard, right before the camera switches to Von Doom picking at his scar, you can see that Mr. Fantastic already wrote 4= Sxlo -4 and underlined it. When the camera goes back to Mr. Fantastic after the picking of the scar, he is now writing 4= Sxlo -4 and underlining it. (00:51:05)
Continuity mistake: Vic offers to take Sue's things to one of his condos. While he says "You'll have 'round the clock care'" he is holding dark-colored pants. The camera cuts to Susan while she says "Thank you, thats very generous." When the camera cuts back to Vic, he is now holding blue pants with a light-colored shirt wrapped around it. (00:44:25)
Continuity mistake: Just before Victor Von Doom proposes to Sue Storm, he kisses her on the hand. He holds her hand near his face, but in the next shot, it is down near his waist. (00:10:20)
Continuity mistake: In the scene where Vic shows Sue the world from the ship, it goes to a shot where Reed finds a problem, when he says "thats impossible it should be 7 hours", The screen show H2 9.44, the next shot it changes to 9.44, the H2 is gone. (00:11:10)
Continuity mistake: When Doom and Thing hit the pool, just before they go through the floor, the guy trying to get in his door (last door on the left) goes missing for a second when the water goes down the hall. And then the guy is back fumbling with his card and goes into the room just in time. (01:28:45)
Continuity mistake: When the blind woman is leaving the pub, her seeing-eye assistant is bringing her to the door. The woman turns around to say goodbye to The Thing again, her whole body is facing him. When the shot goes to Thing's face & then back to her, she is looking over her shoulder at him. (01:05:50)
Continuity mistake: There is a boat coming into shot just as the ladder on the fire truck stops extending over the river. The boat is not seen in any other shots.
Continuity mistake: In the scene where Mr Fantastic walks in on Invisible Girl as she steps out of the shower, we see her covering up with a red towel, but in the next shot, it's a brown towel. (00:55:45)
Factual error: When Reed and Sue are testing the Human Torch's powers, they claim that a temperature as high as the Human Torch's (5000 K to 6000 K) will "ignite the atmosphere and destroy all life". This is incorrect. Many experiments in the lab and on the field have produced temperatures several orders of magnitude larger than the temperature of the Human Torch on a similar scale. Nuclear explosions can generate temperatures in excess of 8000000 K, and temperatures produced by the largest X-ray generator (the Z machine) have been as high as 3700000000 K. Such tests have not ignited the atmosphere.
Other mistake: Johnny picks up Sue's clothes and hides them in his jacket after she strips on the bridge, but when the shot changes to the stunned crowd, we can see Reed and Johnny running off to the left. From the way Johnny's arms are moving, you can tell he is no longer holding the clothes.