One of the greatest scenes in modern movies, and totally improv'd. Harrison Ford had dysentery so bad that he'd been in the hospital for days. They had one day left on their Visas and needed to get that shoot in. Indy was supposed to draw the sword he'd picked up and fight the guy for a rather long and running battle through the streets. Ford, barely able to stand up, muttered something under his breath (caught on camera), pulled the pistol and fired. The stunt man with the sword thought it was a rewrite and reacted very well.
Spielberg said "Cut, that's a take". Ford collapsed. Spielberg's next words were "get him to the hospital and back on a plane."
A slightly modified version, for wiki:
http://indianajones.wikia.com/wiki/Arab_Swordsman
