Godzilla's look radically changes in closeups when he is portrayed by a hand puppet rather than a suit. This is most apparent when he is seen from the front: the suit has a very wide head with noticeable ears, whereas the puppet's head is more narrow and the teeth are far more crooked. The eyes also look different.
Godzilla is mistakenly called Anguirus in the documentary film.
In this film, Godzilla's dorsal fins do not light up when he charges his atomic breath, even though they do in practically every other film in the series.
When the authorities first inspect the dinosaur book, there is a picture of Anguirus in it (inserted into it by the filmmakers). When the book is being read later in the same scene, this picture is gone and replaced by a drawing of two Trachodons (which was the picture that was actually printed in the book).
When Godzilla smashes the lighthouse with his tail, in the closeup of his tail doing that, the model is much smaller than the one in the wide shot after he has smashed it.
In the film when Osaka's blackout is put into effect, all of the lights in the city turn off, including car lights.
In the film's final battle, the strings holding the plane models are visible in several instances.
In the film when a few people are washed away by a flood in an underground subway station, they appear to be transparent, as their images were apparently printed upon the background where the flood was actually filmed.
When the jets find Godzilla on the snow-covered island and fly above him, it is clear that he is actually an unmoving model.
When Godzilla breathes his atomic breath at Anguirus, it is clear as the Sun that the footage of Anguirus' head has simply been pasted over some footage of buildings being destroyed. He also moves his head around in a very unnatural (and quite goofy-looking) manner.
Early in the film during the scenes in the Osaka night club, stock footage of a stage performance from World War II is used. On the left side of the screen, the Japanese red sun banner is shown and next to it is a swastika banner. This would not have happened in the post-war years. Some versions of the film have the swastika blurred out with a gray circle.
During one of Godzilla and Angurius' fights, you can see where the Godzilla hand puppet ends and the technician's arm begins.
The scout pilot in the beginning of the film calls in that there is a school of tuna sighted at 34 degrees N 136 degrees E. This is actually forested mountains, not open ocean.
(at about 10 minutes into the film) When debris is falling on the two scout pilots, one of them tries to shield his eyes with his hand instead of simply lowering his goggles.