What makes ABBA so irresistible?

It only takes a single exposure, and in an instant, your whole day can change. The infection is rapid and feels potentially unending. One minute you're minding your own business and the next you find that you can't stop thinking, humming or singing "Dancing Queen."

"Friday night and the lights are

low ... "

No matter what you try, you can't shake it. In fact, once you start thinking about ABBA, you're a goner. Next thing you know, you've moved to this: "If you change your mind/I'm the first in line ... "

And like the lyrics to "Waterloo" remind us, you couldn't escape if you wanted to.

What triggers this phenomenon isn't always obvious, but it's no doubt about to happen on a widespread scale.

"Mamma Mia!," the film based on the Broadway musical built around ABBA songs, opens in theaters today. As people leave the cineplex belting out the tunes sung by stars Meryl Streep, Pierce Brosnan and Colin Firth, the ABBA invasion will begin anew.

"Mamma Mia, here I go again/My, my, how can I resist you?"

ABBA's songs continue to endure as what scientists have dubbed "earworms" 35 years after the band's first album was released. Like those little bugs, the tunes burrow into our brains and keep hitting the repeat button.

With all this renewed interest, we wondered if it was possible to break down scientifically why the music is so irresistible. Because even those who profess to dislike the cheery pop of the Swedish masterminds can't block its infiltration into their inner jukebox.

Of course, what makes ABBA songs catchy is to an extent what makes most music memorable, from Bach to the Beatles to the Bernie & Phyl's jingle. But, says Daniel Levitin, author of "This Is Your Brain on Music: The Science of a Human Obsession" and associate professor at McGill University, there are some individual factors.

"For one thing, the way their songs are performed and produced, quite apart from the underlying composition, gives them an overall catchy sound," says Levitin, a musician and former producer whose forthcoming book, "The World in Six Songs: How the Musical Brain Created Human Nature," further explores the music-mind connection.

The multitracked harmonies of singers Agnetha Faltskog and Anni-Frid Lyngstad awaken the part of our brains in which our inner caveman is still enjoying a Paleolithic hootenanny with the rest of his clan.