When Meg Maud opens her window and sees Helene her chin and nose are normal. When she's inside with Helene her chin and nose have their prosthetic extensions on.
Professor Olinger is holding his glasses while Ratcliff has Diana under but in a close up he is suddenly wearing them.
The "stone" wall shakes noticeably during Gobbo and Pendragon's scuffle in the Tower of Death.
In the final scene in the lab, the camera shows the empty clothes sitting in the chair far in the background. They were to be a shocking revelation in a few seconds, and that spoiled the surprise.
Lydia's dress sports a zipper in the back.
One of Smolkin's grimly comical songs includes a lyric about "a coffin full of germs". Pasteur's germ theory of disease is many centuries ahead of this film's medieval setting.
When a knight gets knocked unconscious, the man who knocks him out is wearing a wristwatch.
When Livia is trapped under a metal mug while disguised as a mouse, the wire used to make the mug move is visible.