While shark photographers filmed footage in Australia to give Spielberg a realistic underwater cage scene, a wild shark appeared and decided to try its hand (fin?) at the movie business. The shark pounded the hell out of the cage, eventually getting itself tangled in the cables. There was a problem: Neither Hooper or a dummy representing Hooper was in the cage while the shark was going ape in a mess of wires. The footage of a terrifying shark going bonkers was great, but unless Hooper was wearing an invisibility cloak, an empty cage messed up the narrative. So Spielberg rewrote the script, having Hooper swim away in time and thus survive the movie. Even better, he escaped the fate worse than death which claimed Roy Scheider: the sequels.