The helicopter that brings Dr. Doom to the glacier (for his first meeting with the Surfer) is heard to have the classic "rotor chop" sound. Yet the rear rotor is shown to be enclosed, a design which eliminates the "chop-chop" sound.
While Johnny's being examined after interchanging powers with Susan, we can see two incorrectly positioned radiographs on the wall: a posteroanterior chest view that's flipped horizontally, and a simple abdominal one that's flipped vertically.
In the beginning at the airport on the news channel, the anchor woman talks about Reed and Sue's wedding, and it shows a picture of Reed and Sue, Sue has brown eyes in the picture. They also show the same picture of Sue and Reed on the front page of the newspaper.
When Johnny is in the kitchen talking to Ben before the wedding, he is not wearing his tux jacket and you can see he only has a t-shirt on under his dress shirt. Yet when he leaps off the building to chase after the Surfer, his clothes burn off and he is wearing his Fantastic Four outfit/costume, which was clearly not wearing under his tux.
As Von Doom lands his helicopter on the slab of ice to meet
the Silver Surfer, the helicopter points toward the left side of the screen, but a few moments later, after the cut scene to the hole, the helicopter is seen pointing towards the right side of the screen. Another cut to the hole and back, the copter is back to facing the left. Also watch the speed of the rotors. As Von Doom initially leaves the chopper, the blades can be seen rotating slowly. When the Silver Surfer later rises out of the hole, the blades have sped up considerably.
When Victor Von Doom lands his helicopter and gets out, it shows a clip where the blades on the helicopter are moving slow. A few seconds later, you see another clip in which the blades are going a lot faster. Then, after the Silver Surfer comes out of the crater, the blades have completely stopped.
During the first aerial shot of Sue and Reed's wedding you can see the shadow of the helicopter used to film this shot. The shadow is different from the helicopter in shot because it has the spherical shaped camera on the front.
When setting up the machines for the tachyon pulse in the Black Forest in Germany, Thing comes across a bear which is in fact a grizzly. The grizzly is native to North America, and only occasionally found in Europe, certainly not in Germany's Black Forest.
After the Silver Surfer creates the huge hole in the Thames river, the bed is shown to be empty both upstream and downstream. But the entire river from upstream should have been shown to be emptying down into the hole.
General Hager and the rest of his "army" troops are shown wearing blue Navy camouflage uniforms in several scenes (such as Black Forest and Research facility). Captain Raye is even wearing Navy Rank insignia on her collar. United States Army personnel, especially generals, have no reason to don Navy uniforms.
During the opening sequence, when the Silver Surfer freezes the ocean, the logo displayed on the boat is of the "Maritime Self-Defense Force" (a Sun disc with 16 rays on a
white field) of the Japanese flag instead of the single red disc "Hinomaru" version for civil boats.
Whenever Ben turns into the Thing, his voice changes as a result of the change. Johnny's voice does not change at all when he temporarily adopts Ben's powers. However, since this "science" is make-believe, it can do whatever the writers decide.
Fantastic Four established that only the F4's suits (having been exposed to the space-cloud's radiation) can accommodate their abilities. However, in this movie, all clothing of Mr. Fantastic's elongates with his body. Being a great inventor, he could have made extra clothes to suit his abilities.
During Reed and Johnny's "let's have a bachelor party"
conversation scene in the lab, one of the shots is a mirror image (identifiable by reversed text on one of the book covers on the desk.) It is a flipped shot of him pushing away from the desk on the other side later in the scene.