12 Unsolved Movie Mysteries That Drove You Mad

5. Was Prot Really An Alien? - K-PAX

The crux of this 2001 sci-fi mystery film revolves around prot (Kevin Spacey), a psychiatric patient who claims to be an extraterrestrial entity from the planet K-PAX, all while psychiatrist Dr. Mark Powell (Jeff Bridges) tries to prove that he's merely a delusional human being.

The film ends with prot planning to leave Earth via light-travel, and at the stated time of his departure, Powell finds prot's human form catatonic, suggesting that prot has indeed exited his body and returned to his alien civilisation.

Furthermore, prot promised to take a fellow psychiatric patient on his journey with him, and lo and behold, one of the patients inexplicably disappears from the facility at the time of prot's "departure."

There's pretty solid evidence both for prot being a troubled human and an alien. Spacey, for his part, said of his process behind playing the role:

"I really had to approach the film almost on two separate tracks in order for the ambiguity to work," explains Spacey. "I fully believe in Prot as an alien from K-PAX, and I fully believe in Robert Porter as a human being."

The sheer number of contrivances that occur throughout the film suggests that prot probably is an alien, but it's nevertheless a debate that continues to bug film fans.