To some the mouth is just the beginning of the digestive system. A place to gulp oxygen and expel waste gas. An instrument to bestow affection on your nearest and dearest. But to others, it's a V12 engine/dump valve/clunky gear change/any other mechanical noise that needs replicating.
We thought it was just some of the Top Gear office that humbly sit at their desks humming the sounds of an F1 engine at 13,000 rpm like a drunken Crazy Frog. But then we went on the internet and found others doing it. And a lot better than we can.
Below are some of the best renditions of various cars, engines and mechanical noises from the double you double you double you.
We've seen more good ones online, but because we're a family site, we can't put them up as they contain naughty words. But feel free to share your favourite ones below dot commers (and thanks to our upside-down colleagues at topgear.com/au for the links).