It’s impossible to forget this tune once you’ve heard it because it lives inside your head for ever and will pop back whenever you hear the word Milkshake for the rest of your life.

But I had forgotten quite what a strange song it is musically, thanks to songwriters and producers The Neptunes – aka Pharrell Williams and Chad Hugo.

There’s the low groan of the synths that sound as if they are expiring behind the belly-dance rhythm of a lone darbuka (an Egyptian drum), interspersed with the ding of a manjira sample that sounds like the bell on a hotel counter.

It really is a one-off.

But really all we’re listening to is Kelis and those suggestive lyrics that convey something sexy without quite making it obvious; the listener can decide what her “milkshake” really is that brings all the boys to the yard.

“It means whatever people want it to; it was just a word we came up with on a whim, but then the song took on a life of its own,” she said on one occasion. On another she added: “A milkshake is the thing that makes women special. It’s what gives us our confidence and what makes us exciting.”

Jake Nava’s video takes it further, with Kelis playing a waitress in a diner – somehow always sexy – and, at one point, putting her lips around a cherry, which causes a mother to cover her child’s eyes, and dancing around with a posse of dancers in skimpy uniforms.

Meanwhile the cook – played by rapper Nas – starts delivering milkshakes to the customers and, inevitably, the milkshake machine then starts spurting milkshake all over the customers as more and more people enter the “yard.”

“Warm it up – the boys are waiting.”