Revealing mistake: When Flash is rescuing Barin from falling into the void, he rubs against one of the spikes and it bends as if made of rubber. (01:12:55)
Continuity mistake: Klytus is killed when he falls onto three spikes on the platform. In subsequent shots, the spikes that have pierced his body are gone. It can be most seen a minute later into the film, when the platform tilts upwards. (01:15:15)
Continuity mistake: When Flash sits down at the controls of Ajax, the display in front of him is coloured green. When he shows the timer to Vultan later, it's coloured red. The display also goes blank in one shot, after the windows are blown out. (01:31:05)
Continuity mistake: When Flash is restrained in Ming's dungeon, he has a spiked headpiece on, preventing him from seeing. The spikes on this headpiece change position from shot to shot during this sequence in relation to his tied-up arms - i.e. the headpiece keeps being turned, and then is back in position again depending on the shot.
Continuity mistake: The colour of the lighting shining on the archway wall behind General Kala changes from white to green. (00:41:40)
Continuity mistake: When Flash, Dale and Zarkov first land on Mongo, the shots from inside the ship show Ming's guards walking right up to the ship's window and looking inside. When it then cuts to an outside shot, the guards are much further away.
Revealing mistake: Just after Vultan evacuates War Rocket Ajax leaving Flash on board, there is a shot of the rocket heading towards the camera. There is a green-tinted box surrounding it that the special effects team forgot to remove, after it had been rendered against the background. (01:36:05)
Continuity mistake: When the Barron and Flash are fighting with the whips, they hit each other and cut each other on the arms, hands and face, but in the scenes after the fight, neither one of them have so much as a scar where they were once cut.
Continuity mistake: When Barin and Zarkhov are listening to the Colonel on the video screen, the smoke from the control console appears and disappears between several shots. (01:36:35)
Continuity mistake: When Klytus' ship arrives at the Hawkmen city, it is seen hovering in the sky. In the next shot, it is moving forwards, further away from the city and at a different angle. There is also no engine flare at the rear, which would signify movement. (01:14:00)
Continuity mistake: When Ming is impaled on the nose spike of the Imperial craft, the spike is perfectly horizontal. When he eases himself off the spike, it is pointing downwards much more.
Factual error: A meteorite falls onto Munson's bed, setting fire to it. He covers it up with blankets. But the meteorite is still red hot and would surely burn through, and set fire to his bed again.
Other mistake: When Hans Zarkov is having his mind scanned we see tons of images flash by. The one for "Space scientist fired" is several paragraphs long but only the first one was about Hans. The rest is about a leash law in Wellesley, MA.
Continuity mistake: While Dale is watching the destruction of the palace, her head is either tilted or looking straight, depending on the angle.
Continuity mistake: In Arboria, while Aura kisses Barin she says "I brought you a present", then her left arm swaps from being up to down between angles.
Revealing mistake: When the spaceship flies, Zarkov keeps warning about the g-force and Dale and himself suffer it, yet when he tells Flash to step on a pedal, Flash manages to lift his foot and do everything effortlessly, g-force magically gone.
Continuity mistake: When Flash is seated inside the gas chamber and a hood is being put over his head, he swaps from facing to the left to straight between one frame and the other.
Revealing mistake: When the movie ends and the Hakwmen say thanks, watch for the people on the far left: they become greenish transparent because of the blue screen.
Continuity mistake: During the plane flight, the sky outside keeps switching back and forth between cloudy or puffy clouds opening to let a red light, depending on the angle.
Continuity mistake: The hot hail that falls on the hood of Flash's car disappears in the later shots.
Answer: Spider.