The "Into the Woods" star sings in the forthcoming "The Last Five Years" and "Pitch Perfect 2" and she'll take part in a special performance during this year's Academy Awards. So, the actress stopped by "Conan" on Thursday and professed her love for carrying a tune.
"I love it so much and this is near and dear to my heart," she said of "The Last Five Years," which opens Friday.
"It's a very small story about a marriage that's falling apart and this music is so incredible," she added. "I want people to experience it even if it's a different version. ... It's so incredible, the material is outstanding."
O'Brien was taken by musicals' inclinations to spontaneously burst into song and pondered why they couldn't just do it in real life.
"If I could live in a musical, I would," the 29-year-old actress said. And O'Brien made it happen.
"Wouldn't be wonderful if life were like a musical and we sang to each other all day long," O'Brien sang.
"Yes, it would be wonderful if life were like a musical and everything we said was all in song," she continued.
Watch the clip to hear the rest (and Kendrick's killer punchline) and take a second to appreciate O'Brien's unexpectedly stellar voice.