Brad Pitt's specific demand

Although Brad Pitt was eager to take on the role of David Mills, he had one non-negotiable condition before signing on.

The actor insisted that his character would never actually see his wife Tracy’s head in the film’s shocking finale - and he made sure this was guaranteed in writing.

He recalled: “I said, ’I will do it on one condition - the head stays in the box. Put in the contract that the head stays in the box.’”

Tracy was played by Gwyneth Paltrow.