"The Avengers" has so many cool scenes in it that it's hard to pick favorites, but there's no question that some of the best spring from the chemistry between Scarlett Johansson and Mark Ruffalo. Between the epically tense recruitment scene and the terrifying chase sequence they share later, Johansson and Ruffalo ignite the screen every time they share it.

Which is why we're so bummed to hear from indieWire that Johansson has just dropped out of the Judd Apatow romance "Can A Song Save Your Life" and wilol be replaced by Keira Knightley. Looks like we'll have to wait until "Avengers 2" to see Johansson and Ruffalo make beautiful music together again.

Not that Knightley is exactly chopped liver; after all, any time you can add an Oscar nominee to your cast, it's usually a good thing. Chalk that coup up to the power of Apatow, who will be producing for "Once" director John Carney.

So just what will Knightley be doing in "Can A Song Save Your Life?" Well, singing, for one: Knightley will pay a wannabe singer making her way through the tough New York City bar scene when she is discovered by Ruffalo's down on his luck record producer. Naturally, sparks fly, which leads both to romance and to tension between Knightley and Ruffalo's daughter (played by "True Grit's" Hailee Steinfeld).

"Can A Song Save Your Life?" We're not sure about that, but it looks like Keira Knightley can save this movie. And that sounds like music to our ears.