Dutch scientists have developed a system for stopping "racist chanting" at football matches: they feed back the audio of the chant at a slight delay, and the resulting confusion makes it impossible for mobs of football hooligans to synch up their shouting with one another, leading to chaos.
The volunteers were surrounded by loudspeakers that simulated the sound of a chanting crowd and were asked join in. However one speaker replayed the crowds chant with a short delay.
When the delay was greater than 200 milliseconds the volunteers found it too difficult to chant coherently. Increasing the delay, up to about 1 second, was even more effective. "It was very confusing," van Wijngaarden says.
(via We Make Money, Not Art)
