WHOA Ellen Page, whoa. That was first.
This is second. Even knowing what this movie was about prior to viewing it, I was still completely shocked. It was an edge-of-your-seat-where-the-hell-is-this-going movie that had me too terrified to look away.
Third and last. I recommend this movie. I do not recommend watching it on a train where other people around you may be able to catch glimpses of what's happening on screen, as my friend and I did. We more than once paused it, stared at each other in disbelief for awhile, debated whether to continue, and then started up again.
Let's leave it at that.