In the scene where Camille is lying bloody on the ground after the motorcycle accident and James Franco is trying to help her, his shirt is white with a little blood. It cuts away and he is seen again with his shirt completely covered in blood. Cuts away again and his shirt is again mostly white with blood stains, cuts away again and it's completely bloody again.
When Silas and Camille first arrive at Niagara Falls, there is a wide shot of the falls with a group of people standing at the fence (at roughly 18:00 left in the film). This shot is actually a continuation of the final scene of the movie and so takes place AFTER everything else has happened.(During the shot in question, you can clearly see Camille's uncle standing at the front of the crowd with his hands spread, just as he is at the end when the rice is supposedly raining down.)
At the very end of the movie, where Sheriff Foster is at Niagara Falls, His name badge is reversed/mirrored. (The film may have been reversed on purpose to add to the sense of surrealism.)
All of the scenes set in Niagara Falls, New York were actually shot in Niagara Falls Ontario. When Silas is walking across the bridge to cross into Canada, he is actually walking from Canada to the United States of America.