Think about improvisation in movies and chances are your mind goes to anarchic comedies like Anchorman or quick-witted action movie quipsters like Ryan Reynolds.
Horror, however, is not so well known for off-the-cuff spontaneity. Something about a genre full of sharp implements, blood and guts, makes it require a certain amount of careful planning. If going off-script has the potential to be hazardous to your health, then maybe it's worth an actor thinking twice before doing it.
That is not to say, though, that horror is completely scared of making things up on the spot. It might be rarer than in a comedy, but some of horror's most quotable lines and memorable sequences were completely unscripted. (The hybrid genre of horror comedies, meanwhile, is full of improvised moments, from Young Frankenstein to Shaun Of The Dead).
Just look at these ten classic horror moments that were ad-libbed on the spot to see the lasting impact a little improvisation can have.
10. The Helicopter Crash - Attack Of The Killer Tomatoes!
This knowingly silly B-movie about a salad ingredient gone bad may not have acquired quite the same classic status as some of the others on this list. But it did kickstart a genuine multimedia franchise with a George Clooney-starring sequel, animated TV series and more than one video game. It also contains one of the most audacious pieces of improv in horror movie history.
Killer Tomatoes was a predictably low cost affair, but they did manage to scrape together the funds to hire a helicopter to land in the background of a scene of cops gunning down mutant veg. But as the little chopper came in to land it spun wildly out of control, crashing in the field.
For a film whose budget barely stretched to six figures, wrecking a $60,000 helicopter was less than ideal. But the cameras had kept rolling, giving them some unexpectedly dramatic crash footage. How could they not throw it into the movie?
While going over to help the thankfully uninjured actors out of the wreckage, director John DeBello decided to shoot some footage of them crawling clear. He even prompted actor Jack Riley to improvise a line about kamikaze tomatoes to explain the seemingly random background accident.
Over the years, the crash has become one of the cult movie's most memorable scenes: an unexpectedly real action stunt in a cheap nonsense parody.