Significance? Well, in the movie, we learn that the further the heroes dive into a person’s subconscious–into a dream within a dream within a dream, and so on–the more slowed-down time becomes. So if composer Hans Zimmer is playing us a super-slowed-down version of “Non, Je Ne Regrette Rien,” then the implication is that we’re still submerged deep within the dream, far from the kick that will wake us up.
“You realize that the elements that we’ve extracted from the Piaf song are the way you get from one dream level to the next,” Zimmer said.
The charged symphonic brass of Piaf’s “Non, Je Ne Regrette Rien” was targeted for use by Nolan yet almost dropped from the film when Marion Cotillard, who starred as Piaf in 2007 film “La Vie en rose,” was cast as Cobb’s wife, Mal. Zimmer, however, said he talked Nolan into keeping the song in the film, arguing that audiences would not be distracted by the connection.