The princess has modern tan lines in her nude scene.
When the fanatics parade through the village, rolling a huge wooden wheel before them, a stack of camera equipment, partially covered with a blanket, is visible in the background.
During the fight in the quarry near the end of the film, when a knight falls off his horse, the side of a white prop truck is clearly visible behind him.
At the end of the film, visible wires hold up the monster's head.
Potatoes originated in the Andes, in South America. They were introduced to Europe in the middle of the 16th century, and were a staple food about 100 years later, well after the feudal era.