20 Things You Didn't Know About Die Hard

12. Many Scenes Were Improvised Due To The Ever-Changing Script

Despite how incredibly tight and intricate the final movie appears to be, Die Hard's shoot itself was shockingly off-the-cuff at times, to the extent that the film's ending hadn't even been nailed down before filming began.

Much of the dialogue that made it into the final film was improvised by the cast and crew, as the screenplay was being tweaked on a day-to-day basis.

Furthermore, sets were even constructed before the scenes within them were written. The computer room, for example, where Hans memorably quips, "Shoot the glass," was built before anyone knew exactly what it would play host to.

Though the improv miraculously paid off, it did result in a few iffy production issues, namely the ambulance which drives out of the terrorists' truck being too big to fit inside it, requiring McTiernan to cleverly edit around it.

But again, the end result largely feels so meticulous that you'd never know just how much of Die Hard was a seat-of-your-pants effort.