Other mistake: In the Forbidden Forest, after Grawp has put Hermione down after grabbing her, he turns round and bends down to pick something up. When the shot turns to Ron, Hermione and Harry they are still looking up at Grawp even though he's bending down. Their position doesn't move. Ron even looks Grawp up and down, even though he's still bent over with his back to the students. (01:27:10)