When Will Turner, Norrington and Jack Sparrow are fighting inside the wheel as it rolls through the forest, one section of the fight is viewed from the side. The wheel's rotating very quickly and the ground is spinning round to add to the effect, so it's difficult to notice at normal speed unless you're looking for it. In slow-motion it's easy to see that at several points they're standing in positions that would in no way allow them to maintain their balance. The scene was clearly shot in front of a green screen, and the motion of the ground hasn't been synced up properly to make the gravity work, so they stand at some very weird angles.