Other mistake: Radio aerial visible on building. (00:09:40)
Audio problem: In part II, after Cohen has killed the High Priest he sheaths his sword. You can see that he actually misses the scabbard, and slides his sword down the side of it, but the sound of the sword being sheathed can still be heard as the camera pans to Rincewind.
Other mistake: Throughout the movie there are mistakes concerning the position of the star towards the turtle and towards the people on the Discworld. When the turtle is flying directly towards the star, then it should be seen by the people on the horizon and not close to the zenith. Or - at the end - when everybody is watching the babyturtles hatch out, A'tuin turns around. But the people are still watching the phenomenon looking in the same direction as before.
Continuity mistake: When Rincewind and Twoflower are at the Edge, Rincewind tells how he only knows the one spell from the Octavo and how he got it. In several shots of Twoflower the clouds in the background change drastically, often between one- and two-seconds shots of Rincewind. The clouds are almost motionless in every shot, so they could not have drifted that fast so suddenly.
Revealing mistake: When Cohen complains about how nobody takes him seriously because he doesn't have teeth anymore, you can see a full set of teeth in his mouth.