The Tin Man in The Wonderful Wizard of Oz (1939) is looking for a heart, a humanity, which in fact he already has within him.
The actor who played this character was originally going to play the scarecrow. They swapped roles. He became seriously ill because of the paint on him, which was highly toxic. He was unable to play the role and was replaced by another actor for whom the make-up was changed. The latter suffered an inflamed eye but managed to play the role.

Difficulty ****
A simple hypothesis will help you to make it.