Sure, Lively was joking about a polygamist marriage between her, Letterman, and Julia Roberts, but the electricity between the Gossip Girl star and Letterman as strong and real as that time one year ago when Lively said Letterman was in the same league as Leonardo DiCaprio, and he kissed her hand.

The on-air flirtation this time didn't quite reach Letterman-Drew Barrymore levels, but between the thigh groping, chin touching and hair twirling, Letterman was primed to laugh at Lively's dog story like it was told by Robin Williams.

Lively made sure Letterman knew she was free — some sort of vacation — in a week. One week. Seven days.

Or about how long Letterman has been married, and how long he'll be taking cold showers for.

When you get right down to it, it's not surprising why Dave took such a fancy to Blake. After all, she's young (20 years old), tall (5'10") and blonde. Um, there's also the fact that she's totally into him! Witness how her body language changes from the time that she sits down to the time that Dave clasps her hand and then kisses it ever so gently. Blake may be young in terms of age, but she plays the moment like a showbiz veteran; mere seconds into the interview, she has Dave eating out of the palm of her hands. And kudos to Dave for playing along, especially considering that interviews like this likely result in him catching all kinds of flack from his babymama. Even though nothing will likely ever come from this moment of televised flirtation, it's moments like this where we are reminded for the umpteenth time why we tune into watch Dave every night instead of Jay.

• Late Show With David Letterman [CBS]