In the scene when Ethan breaks into the CIA HQ, you can see a shot of his head and upper-body coming straight down through the ceiling. This is impossible because you then see the other agent lowering him down into the vault. The rope is let down over a pulley on the edge of the vent, so when Ethan's head is coming through the vent, the pulley that is holding him is at the same hight as his shoulders.