The moment I've figured out the twist (spoilers)
I didn't know anything about this film before I started to watch. The 1st twist caught me by surprise (when the girl found the other boy in the basement).
However, as soon as the girl googled the name Jason and found out he's kidnapped , I just knew it. I knew that "Andy" is Jason. It all started to come back, like mother getting angry when he said he wanted to practice walking, when she cared for the little basement boy beyond reason (at that point the audience should still be thinking the basement boy was there just for organs). And when mom started to practically bullying Andy, they gave it away for everyone, I think.