In the final battle where Wolverine is thrown by Colossus at Magneto as a diversion so Beast can attack from behind with the anti mutant darts.

Watch how the position of the darts change. When Beast first stabs them into Magnetos chest they are pretty much in a straight line going across. Magneto then talks to Jean/Phoenix and in the next scene when he takes them out they are in a line down his chest. This mistake is quite obvious.