A sneak preview of episode seven of season four of Grey's Anatomy, entitled "Physical Attraction, Chemical Reaction." Meredith and Alex discuss his hooking up with Lexie. George and Izzie confide in Mer about sex with the other.
Meredith: [narrating] Before we were doctors, we were med students, which meant we spend a lot of time of studying chemistry. Organic chemistry, biochemistry, we learned it all. But when you're talking about human chemistry only one thing matters: either you've got it or you don't.