It is based on a descending chromatic scale followed by variants of the same phrase in first the minor and then the major key, corresponding with the vicissitudes of love expressed in the lyrics.
It has also been arranged for various instruments, and one of my favorites is the arrangement for two pianos done by piano duo Anderson and Roe (jump to about 3:35 for the Habanera theme) and filmed in both the concert hall, with concert grands, and an intimate garden setting on upright pianos:
And then there’s this version, filmed in an old warehouse:
The latter is a clearly nuanced interpretation, with Beaker’s clear soprano declaiming the lines “MEEP MEEP MEEP” and the Swedish Chef’s steady underlying rhythmic background. Animal provides what would be originally the chorus’s interlude, and he provides it with character.
rah rah rah RAHHH!
Beaker’s rose is also a nice touch.
All in all, a truly thrilling performance.