If you haven’t yet worked this out from the trailer of The Kids Are All Right, which, annoyingly, like all movie trailers these days, gives away the entire movie, lesbian mom Julianne Moore gets it on with her kids’ sperm-donor dad, played by Mark Ruffalo. What you don’t see in the movie, though, is the extreme hilarity of their sex scene. And, well, Mark Ruffalo’s many sex scenes. At the movie's New York screening, we had to ask Ruffalo how one prepares for something like that. "You just kind of dive right in," Ruffalo told us, "and let nature take its course. If you’re relaxed, you can sort of play. A lot of that was improvised. When she’s holding my face like he’s a riding pommel, that was all Julianne. It’s so crazy. You’ve never seen sex like this. Well, maybe you have, but not onscreen." For more celebrities talking sex, click through our Party Lines slideshow.