In the scene where the wargs attack the refugees from Edoras, after Aragorn has fallen over the cliff (to be precise in the minute and second of the theatrical version and 12th minute and 37th second of the second disc of the extended version) you see a whole heap of Rohan Riders finishing off the wargs but there is one Rider in the bottom left hand corner of the screen who swings his swords around and stabs the air!