Answer: Cricket Fans

Although computer rendered sets and computer generated sounds might have firmly embedded themselves in modern film making, there are some things that are best approximated by real live people. Some things, such as the chanting of thousands of orcs.

When filming the Lord of the Rings film The Two Towers, Peter Jackson wanted the chanting of the orc armies to seem as real as possible. The only way to recreate tens of thousands of soldiers hollering and chanting without resorting to lots of digital trickery, then, is to record tens of thousands of people actually hollering and chanting. To that end, Jackson and his sound crew showed up at a cricket match in Wellington, New Zealand at Westpac Stadium. Jackson instructed the energetic crowd of 20,000 cricket fans, who were more than happy to oblige, and the resulting chorus of yells, screams, chants, and grunts became the sound of the Uruk-hai orcs rallying before the Battle of Helms Deep.