Revealing mistake: At the beginning, when the woman in the flotation seat is paddling backwards, you can see a fishing line attached to the back of seat that is being pulled to help her move backwards.
Revealing mistake: When Anguirus makes his sacrificial charge against Gigan, the hand that is moving the Anguirus costume can be seen holding it.
Revealing mistake: During the iconic dojo brawl scene, Bruce Lee at one point picks up two men and whirls them around. It's obvious in the wide shot that they are just dummies.
Revealing mistake: Just before Louise shoots him, Andrew turns to face the camera, and the blood packs under his shirt are very visibly outlined.
Revealing mistake: When the sword mistresses kill the ninja we see them slice his whole nose off, however when the ninja's dead body is rolling across the floor you can see his nose is still attached. (00:15:32)
Revealing mistake: At the beginning of the film O-Yuki is fighting the men in the forest and kills them one by one. When she kills the last one there is a close-up shot of her dagger entering his rib area and blood sprays out. However, if you pay close attention you can see the blood sprays out of his sleeve (presumably there is a device in there), not his torso. (00:01:18)