Goofs

Godzilla's appearance drastically changes after he reaches the island because a different monster suit was used for the water scenes.

Black vertical connection lines are clearly visible on the sky backdrop in every shot during the monster scenes.

During the fight between Godzilla and the three Kamacuras, the top of the set is briefly seen.

When Riko retreats into the jungle after feeding fruit to Minilla (when she sees Godzilla approaching), the 'person' retreating is clearly a small doll.

The holes in the neck of the Godzilla suit are clearly visible in many shots.

When Riko throws the fruit into Minilla's mouth, the fruit is obviously transparent hand-drawn animation.

In several scenes the strings used to manipulate the Minya, Kamacuras and Kumonga marionettes as well as Godzilla's tail are clearly visible.

How does the Kumonga manage to sting Godzilla in the eye during their climactic fight if Godzilla's head is way up high and Kumonga's stinger is near the ground? They never get close to each other.

Riko takes water from a red lake to treat the fever the scientists are suffering from. But Godzilla and Minilla have just blown their atomic breath beam into the lake, and the whole island was contaminated by radioactive fallout from the scientists' earlier experiment. This would lead people to believe that the lake's water would be highly dangerous to consume. If the water was radioactive, Riko may have presumed that everyone would be rescued very soon and those that drank the water would receive the appropriate medical treatment for radiation poisoning. Also, one often overlooked fact is that Godzilla "feeds" on radiation. His body may have absorbed much of the radiation from his surroundings, thereby reducing the lake water's radiation level to a non-lethal level.