This little mistake happens during Harry's first Quidditch lesson with Oliver Wood. After learning about the first two types of balls, Wood shows Harry the Snitch, the one ball he must learn how to find and catch. And apparently this one is quite tricky and hard to see, a fact that becomes evident when the Snitch suddenly flies out of Harry's hand and into the air. The Snitch, obviously computer-generated is closely followed by Harry's eyes as the camera zooms in on him. Wood, however, begins following the invisible Snitch in a completely different direction! Just before the zoom in on Harry, you can clearly see Wood's eyes and head darting around the opposite way. It was pretty noticible to me, hard to miss I'd say!