On last night’s Late Show, David Letterman asked guest Justin Timberlake why, if he idolizes Frank Sinatra, Dean Martin, and Gene Kelly, he hasn’t done a musical. Turns out, it’s because he doesn’t like spontaneously bursting into song, which, of course, he and Dave then did. Sort of. Watch the clip below. Check out the full interview here. It ends with more singing. Timberlake is promoting his new film In Time, and, together with Dave, he also explained how characters in that futuristic world transfer time to one another by physically grasping forearms. “If I’m on top, I’m taking time, and if your on top, you’re taking time,” Timberlake said. The audience giggled inappropriately. “You know, I have found it to be true that if you’re top, you better take your time,” Letterman cracked. Love these two together.