As you do. When you're part of a Three advert.
Yes, the mobile phone network's quirky ads continue with this cultured mini-flash mob: a small choir appearing at random moments at bus stops, cash machines and other public places - and proceeding to sing the dictionary definitions of words.
Well, we say 'random' - but as you'll see, each definition actually fits in perfectly with their surroundings.
And the point of it all? To celebrate Three making all its 0800 numbers free on its new pay monthly plans. But of course!