Because it's part of the evolution process. Back when all life lived in the sea some species learned how to expel air to help propel them self's onto land. Then some species learned to use that talent for survival - they would expel air to confuse predators. Early man learned to use that talent to help negotiate peace or trade talks - someone would say - hey pull my finger then they would expel air - everybody would laugh and make peace or trade. Cheers and happy weekend!
The sound is from having squeaky butt cheeks rubbing together while walking. A bit of axel grease will solve the problem.
This post was edited by Kittigate at January 19, 2019 6:23 AM MST