5. Red Skull's Face Mask Is Visible In His Very First Scene - Captain America: The First Avenger
Captain America: The First Avenger's primary antagonist is of course Johann Schmidt, a Nazi officer better known by his villainous moniker Red Skull, after becoming horribly disfigured by a primitive version of Cap's Super Soldier Serum.
Schmidt has to wear a face mask to cover his reddened skin, and though this isn't revealed to the audience right away, Schmidt's very first scene at the start of the movie subtly hints at it.
While Schmidt's talking to the church keeper (David Bradley), pay close attention to the skin around Schmidt's left ear, which creases in an unnatural and grotesque way for a moment, revealing the seam of his face mask.
The scene's low lighting makes it tricky to catch, but there are in fact a few sneaky moments throughout the film such as this where Schmidt's mask begins to slip ever-so-slightly.