Make no mistake: Were it not for its serious-as-a-heart-attack subject matter, Songbirds could be the next Rocky Horror Picture Show — Showgirls be damned. What else to do with a musical documentary about real-life British female prisoners who sing songs like "I'm Oh So Very Sorry!" while they dance under a stream of animated blood? I am genuinely curious about where, if anywhere, a movie like this could live, and I do hope it finds some kind of home. "Insane," declared one other critic upon exiting (early) a screening of the film, but I was slightly charmed. Rather than being mocked, the prisoners are compellingly, lovingly rendered — at least until they launch into songs like the ensemble number about international drug trafficking, "Mule It." Then, they're just plain highlarious, and ain't nothing wrong with that.