The special effects for An American Werewolf in London were created by Rick Baker. The sequence in the GIF set shown above earned Baker an Oscar.
The animatronics used to create the two minute long excruciating werewolf transformation were quite elaborate. Several animatronic heads were produced for the facial changes of the shot and consisted of a fiberglass shell, foam and wolf hair. To create movement in the sections of the cheeks and forehead, air was pushed through syringes.
The teeth in the jaw are larger than the actor David Naughton’s teeth, but smaller than the final teeth of the werewolf, which contributes to the scene’s overall effectiveness and realism.
(Source: horroroftruant, via nothingbutamouthfulofgreeksalad)