I didnt google that question but have a theory of my own
They have a chemical imbalance in their brain.......when they walk, they automatically hear the Bee Gees song "Staying Alive" and they are bobbing their head to the beat of the music

(let your imagination run riot, hear the song, and you may find yourself doing the same thing

)
I'm sure there is a more scientific reason.....but i quite like my original thought after reading that question!!
I'm not from America no, I'm from bonny bonny Scotland.....the land of beauty, haggis and braveheart

oh and irn-bru
