Azufre literally means "sulfur," a chemical element often associated with brimstone and hell. It's a very unusual and dramatic word to find in a pop song, making it instantly memorable.
Shakira uses it to create a powerful metaphor, singing about a taste on the skin of "azufre revuelto con miel" (sulfur mixed with honey). This striking image perfectly captures the song's theme: a dangerous, toxic attraction that is also irresistibly sweet and tempting.
Have you ever made the same mistake twice, knowing full well it was a mistake the first time? That's exactly what Shakira is singing about in this song. She describes a wild night in a hotel room with someone who is definitely bad news, a taste of "azufre revuelto con miel" [sulfur mixed with honey]. She knows what's coming, but decides to take a "caminar por el lado salvaje" [walk on the wild side] anyway. The whole thing gets so out of hand that the people in the next room complain to the hotel reception!
The chorus is a classic Spanish expression: "Lo hecho está hecho / Volví a tropezar / Con la misma piedra que hubo siempre" [What's done is done / I stumbled again / over the same stone that was always there]. She admits she's an expert at repeating her mistakes with men, but she also knows why. It's because "Se siente tan bien todo lo que hace mal" [Everything that's bad feels so good]. It's a fun, self-aware song about giving in to temptation, even when you know you probably shouldn't.