(at around 1h 30 mins) As Susan Storm is containing the Super Nova being created by Johnny Storm her nose begins to bleed, but seconds later there is no sign of blood on her face.
(at around 1h 28 mins) When Thing and Doom fall through the pool into the hallway, the guy with the champagne glasses appears and disappears between shots.
(at around 53 mins) As Von Doom is watching Mr. Fantastic on his monitors as he's doing the equations on the blackboards, the final underlined statement is already on the board - then Mr. Fantastic goes and writes it on the board, underlines it, and retracts his arm.
(at around 1h 2 mins) When Johnny Storm is coming out of the motorcycle show, he has his arms round the shoulders of two women. In the next shot he is linking arms with them then in the next shot, his arms are back round their shoulders.
(at around 33 mins) When Sue goes invisible for the first time on the bridge, she has high-heeled boots on as she disrobes. Then suddenly her feet are bare even though she didn't take off her shoes nor is there any sight of them when Johnny picks up her clothing from the road.
(at around 49 mins) When Reed is testing Johnny Storm's ability to "flame on" in a test chamber constructed of titanium, the recorded temperature exceeds 4000K. Titanium melts at 1941K, and boils at 3560K. As there were slots in the chamber walls, it is unlikely that any insulation would have been effective in maintaining the integrity of the chamber.
(at around 49 mins) It is impossible to ignite Earth's atmosphere. All 'burning' chemical reactions between nitrogen and oxygen to form nitrogen oxides are endothermic chemical processes, which means they require continuous energy input to keep them going.
FDNY firefighters wear leather boots not rubber ones as seen in the film.
New York City Fire Department Ladder 54 is an aerialscope style "Tower Ladder" featuring a platform at the end of the ladder, not a "straightstick" that lacks the platform. In fact the FDNY currently has no midmount straightstick in service.
The missile Victor fires at Johnny is so small it could only be a short range heat seeking missile. But it follows Johnny all over the city .There is no way it could contain enough propellant to keep it flying as long as it does.
The chamber that Reed Richards created was unable to maintain its power level without Dr. Doom's power surge. How could Ben make it work after Sue and Johnny left to help Reed. Actually, there is only a need for more power to reverse the effects of the storm. Simply being exposed to the storm once again doesn't require any extra power.
(at around 33 mins) In the bridge scene, Johnny and Reed encourage Sue to turn invisible so she can sneak past some police officers, forcing her to disrobe. After she sneaks past, Johnny and Reed run up to her carrying her clothes, they manage to pass by the police officers themselves since the officers are too stunned by seeing Sue turn invisible to notice.
(at around 1h 3 mins) The Thing throws a license plate at the Human Torch's neck. Given the strength of the Thing, that should've cut his head off. However, Thing is able to control his powers and didn't throw the plate at full strength.
(at around 57 mins) When Von Doom goes to grab a towel in his bathroom he receives an electric shock to his right hand but looks to the left, all other shots in the rest of the scene show him looking left and it being on his left hand. Actually, the shots where he's "looking left" correspond to his image in the mirror of the bathroom, as it's made clear at the end of the scene.
(at around 1h 6 mins) When The Thing walks into the bar his footsteps are heavy enough to bounce the pool table and make the jukebox music jump, yet the drinks on the tables don't move at all.
(at around 1h 20 mins) After Victor changes Ben back to human, he attacks Ben with a backhand strike. Ben flinches just before Victor starts his swing.
(at around 11 mins) When Victor Von Doom is shown proposing to Sue Storm in the space station, for a brief moment you can see a reflection of the blue screens they used to create "space".
(at around 1h 29 mins) When Doom hits Ben with the light pole and Ben hits the ground, concrete from the street comes up before he actually hits the pavement.
(at around 43 mins) When the Thing gets out of the police van, you can see a blanket under the van which hides the hydraulic rams (so the van can move up and down because of the Thing's weight.)
(at around 1h 23 mins) When Dr. Doom is bending Reed Richards finger back when he's super cooled, Dr. Doom's hand slips and lets Reed's finger go at the end of the shot, but it continues to make the crunchy noises as if he is still bending the finger.
(at around 1h) During the motorcycle show you can hear the announcer speak during an overview shot, but you can clearly see that he doesn't have the microphone near his mouth.
The logo for CityTV of Vancouver is clearly visible in a street scene.
In many New York scenes, the Burrard and Granville bridges of Vancouver, British Columbia, are plainly visible.
(at around 36 mins) FDNY Ladder 54 is housed in the Bronx nowhere near the Brooklyn Bridge.
(at around 59 mins) After returning to NY, the 4 are sequestered in the Baxter Building. After a few days, Johnny leaves without notice and he already has new vanity license plates on his car.
The Thing's weight is inconsistent throughout the film. For example, at the beginning, he's heavy enough to collapse a hospital bed while simply laying in it, but when he's thrown into a moving car by Dr. Doom at the end of the film, he does little more than dent the hood and apparently has little impact on the vehicle's maneuverability.
(at around 1h 30 mins) Reed asks Doom a "Chemistry 101" question about what happens when a metal is rapidly cooled. Since there's no chemical reaction involved in cooling metal, he should have posed it as a "Physics 101" question.
(at around 49 mins) Reed and Sue's warning to Johnny about approaching 4000 degrees Kelvin is wrong on two counts. Not only is this not approaching the temperature of the parts of the Sun that actually 'burn' hydrogen (the Core and the Corona, which are a thousand times hotter) but as a single point of heat only the air in the local vicinity would burn - not the whole planet's atmosphere. A far greater risk would be what in fact happened: objects near by would set alight and burn/melt.
(at around 48 mins) When Reed is evaluating the group members, the screen lists Ben's powers as "superhuman strenght" rather than "strength."