Does "Yippee-ki-yay" sound familiar?

Actor Alan Rickman, who died Thursday, might now be most familiar as the mysterious Snape in the "Harry Potter" movies, but he will always be one of the greatest action-movie villains of all time, if not the greatest, in "Die Hard."

Rickman was so great as Hans Gruber, in fact, that the third "Die Hard" made the villain Gruber's brother, which was a bit silly but still worked.

Hans Gruber is the German mastermind of a group of terrorists that's actually pulling off a heist of a giant corporation in the original "Die Hard" (1988). John McClane (Bruce Willis) is, of course, the off-duty policeman who's there to stop them.

The most quoted, most replayed scene of the movie is Gruber's death, when McClane utters his final words to the villain, who then goes falling off the skyscraper with this petrified reaction:

Rickman was a great, one-of-a-kind actor, but the story behind that reaction shot involves more than just acting.

Director John McTiernan asked Rickman to fall backward onto an airbag from 25 feet in the air, to create a scene that felt real. Fair enough, but instead of dropping him on the count of three, the stunt crew let him fly on the count of one, which resulted in Rickman's not-at-all-faked surprise and fear.

That's right: In his best movie shot ever, Rickman kept it real — even if that's not exactly what he intended.

Check out more things you didn't know about "Die Hard," and the full falling scene, below: