On the cover of Oral Fixation 2, Colombian singer Shakira Ripoll cuts an atypical figure. Her rivals in that trillion-selling world where dance-pop meets AOR, and the soul-baring Linda Perry-penned big ballad rules supreme, tend to bare some flesh and smoulder seductively on their album sleeves. Well, Ripoll certainly does the former - she hasn't got any clothes on at all - but there the similarity ends. Her modesty is covered by some deeply unconvincing plastic leaves. She proffers both a quizzical expression and an apple. The apple is being glared at by a baby crawling along the branches of a nearby tree.

Ripoll has provided an explanation for the cover, but then, Ripoll has a way with an explanation that makes you wonder why anyone bothered asking in the first place. This one involves Renaissance art, original sin and a desire "to attribute to Eve more reason to bite the forbidden fruit". Nevertheless, it seems safe to say that you wouldn't get anything similar passing the lips of Christina Aguilera.

Ripoll's last English-language album, 2002's Laundry Service, went platinum 13 times over, but it's not too much of a stretch to suggest that she bears a similar relation to her American pop-AOR peers as the Tropicália artists of late-1960s Brazil bore to British and American psychedelia: their sound has the same basic constituent elements, but is rearranged and amended according to some perplexing internal logic until it resembles something beamed from Mars rather than Latin America. Another way of putting it is that Ripoll is crackers.

Just how crackers is signposted the minute Oral Fixation Volume 2 hits the CD player. Anyone discombobulated by the cover image should spend a few minutes composing themselves before pressing the play button and thus being confronted by How Do You Do. The opening track features mock-Gregorian chanting by a group called Seraphic Fire, a staccato wah-wah guitar solo that bears a debt to Queen's Killer Queen and a winning chorus that you would call stadium rock were it not embellished with backing vocals sung in an inexplicable baby voice. The lyrics seem to feature Ripoll confronting God with his failings - she is angry about famine, she is angry about the Middle East and she is also angry about cats being chased by dogs. For the most part, they are so opaque that they might as well be in Latin, which indeed some of them are.

Any notion that things will subsequently calm down a bit are swiftly rebutted by track two, Don't Bother. The music is more sedate, the topic is love lost and the services of Seraphic Fire have been dispensed with, but even when the sound edges closer to standard pop-AOR, Ripoll's voice and lyrics still offer plenty to grapple with. The former swoops from whisper to guttural scream and, at moments of high drama, employs a vibrato effect that makes her sound like Alanis Morissette being driven over a cattle grid. The latter are so bizarre they occasionally suggest a faltering grasp of English. "For you," she seductively moans, "I'd give up all I own and move to a communist country." On Hey You, a lover is firmly told "don't play the adamant". Ripoll's website reveals that the lyrics to last year's all-Spanish Fijacion Oral Vol 1 are, if anything, even more imponderable. "Te conoci un dia de enero can la luna en mi nariz," offers Dia de Enero: "I met you one January day with the moon on my nose." Que?

Elsewhere on Vol 2 there are surf guitars and elephant sound effects, Britpop oompah and Sergeant Pepper brass, a pastiche of Led Zeppelin's Kashmir and a steal from Radiohead's Creep on Costume Makes the Clown. The climactic Timor answers the question of what Franz Ferdinand would sound like if they employed a children's choir and antiquated "syn-drums" that bring to mind either Kelly Marie's disco hit Feels Like I'm in Love, or early 1980s cartoon Pigeon Street, depending on the listener's age. Admittedly, this isn't a question that anyone other than Shakira has spent much time pondering, but the result is bewildering and exhilarating. And you could happily apply the same adjectives to the whole of Oral Fixation Vol 2.

There are departments in record companies that exist primarily to stop multimillion-selling pop artists doing anything that might affect sales and profits. You suspect that fairly high on the list of things they want to stop multimillion selling pop stars doing is making records that sound like Franz Ferdinand with a children's choir and the drums off Pigeon Street. Quite how Ripoll got past them is intriguing. Perhaps the fact that she already had three multi-platinum albums before singing a word in English gave her a stronger will. Perhaps the intuitive pop sensibility you can hear on every track mitigated the Gregorian chanting and elephant noises. It doesn't matter: Oral Fixation is the sound of an utterly unique voice in a uniform world.