20 Things You Didn't Know About Shutter Island

5. Teddy Only Strikes Matches In The Second Half Of The Movie

Naturally nobody notices this the first time they watch the movie, but on repeat viewings keep an eye out for Teddy's cigarette smoking etiquette, as it holds a major clue to the film's big twist.

In the first half of the movie, Teddy is never seen striking a match to light his own cigarettes, presumably due to the traumatic association between fire and the arson death of his wife at the hands of Andrew Laeddis.

Teddy and his real-life persona Andrew begin to combine over the course of the movie while his treatment takes hold, and so the second half of the film sees Teddy/Andrew wilfully striking matches, notably while lighting his way through Ward C.

At an unconscious level, this symbolises Teddy and Andrew becoming one reconciled personality and him slowly coming to accept his own role in his wife's death. Clever.