The backcloth that represents part of the back wall of the TARDIS control room set in the opening scene is bunched behind the Doctor, destroying the illusion of flatness or solidity.
Although the characters are physically unable to touch anything, Barbara knocks a mannequin, which wobbles as a result.
After leaving the TARDIS, Vicki's shadow is cast against the distance mountains, which are evidently painted on a backcloth.
Ian asks where the crew's 13th-century clothes have gone, but the clothes were acquired during the third crusade in 1191, which is in the 12th century.