The fighting starts when a signal such as an air horn or whistle blows, and can last anywhere from a few minutes to a few hours.

BBC: Get rowdy at International Pillow Fight Day

He loaded the volumes onto a little cart and as he ran he heard the bullets whistle through the air above him.

BBC: Studying history at Kabul University

News of Mr Chavez's resignation caused hundreds of flag-waving and whistle-blowing Venezuelans to surround the city's air force base, La Carlota, in the hope of seeing Mr Chavez' departure from the country.

BBC: Venezuela's new dawn

Earlier this summer an anonymous air-traffic controller filing a report to Chirp, the industry's confidential whistle-blowing agency, claimed that pilots of low-cost airlines were cutting corners to achieve flight timetables.

ECONOMIST: The price of flying on a low-cost airline