Whither love? It's the eternal question posited by everyone from poets to pop stars. And in this episode of N of Us, it's answered with three social psychology studies. Help is on hand from Keanu Reeves and Sandra Bullock, Woody Allen and Diane Keaton, Harry Connick Jr and Donny Osmond, all of whom offer their tuppence on who we fall in love with and how to make it happen.