20 Things You Somehow Missed In Shutter Island
6. The Reverse Cigarette Smoke
Teddy's aforementioned nightmare sequence half-way through the movie shows him smoking a cigarette lit for him by "Andrew Laeddis," before coming across the blood-stained visage of Rachel Solando - or rather, a nurse in the guise of Rachel (Emily Mortimer).
After "Rachel" lets out a scream, Teddy turns and, if you take a close look at his cigarette, the smoke is actually disappearing back into it in reverse.
We see this effect deployed in two separate shots in the sequence, with the clear intent of visually conveying the un-reality of Teddy's nightmare.
It's a fairly basic VFX trick, but honestly, aren't the best tricks often fiendishly straight-forward?