I'm watching a Jekyll and Hyde plot on Dark Shadows set in a parallel universe (which is fairly fitting for a storyline about alternates), but when clean-shaven Cyrus transforms into the evil John Yaeger, he gains a mustache. When he reverts, the stache disappears.
I saw this in a Ferrigno Hulk movie too. Bixby had a full beard which disappeared when the hulk came out to play. That goddamn hulk doesn't believe in beards, and then the beard manifests back when he reverts to human form.
Steven Hawking would be rolling in his