These two extreme frames from the season two He-Man episode "The Arena" show how not to animate a shocked expression! In the first frame we can see a familiar Prince Adam stock cel which we have seen many times before. Now usually to convey surprise the director would call for the animators to simply create a cel overlay of the character's eyes wider. However on this occasion Filmation decide to animate the character's head and the end result is less than appealing.
(click on the images to see them at full-size)