At the beginning of the episode when all of the doctors are standing outside, a doctor in the back can be seen walking out with his lab coat over his shoulder. In the next shot, his coat is on. Another cut takes place, and his coat is now off again, and we see him putting it on.
Between 8.36 and 8.40 you can see that he's wearing a costume. It flakes a bit when Webber falls over the patient. It's a visible mistake when you actually see it.