It's nighttime in Seattle, but not just any nighttime: it's the nighttime of Izzie and George's for reals this time, perfect, awesome, sexy sex. But Izzie looks like it's less than perfect; instead she looks incredible alarmed, staring at the ceiling, naked and sweaty. Meredith's mercifully brief VO begins, "Before we were doctors, we were med students. Which meant we spent a lot of time studying chemistry." George is also lying in bed, really sweaty, and really confused. They make some talk about how "wow" the sex was, and George also comments that it was extremely aerobic, hence the sweat. Izzie asks if aerobic is bad, and he asks it right back, insuring that it was aerobic-really-bad. Izzie tries to make some excuses about them being nervous, while George sits with his hands in the air like he's paralyzed and agrees, laughing too hard. They decide to do it again, and it sounds a lot more like doing chemistry homework than having perfect, hot, awesome sex.
Meredith's voice supplies options. "Organic chemistry. Biochemistry. We learned it all." She and Derek are in his trailer, also studying anatomy. Derek asks her what's new and she nonchalantly replies, "I saw my half-sister naked. What's new with you?" Taken out of context, that could be a situation you only find on certain websites you don't want to visit on a public computer. Derek's night consisted of dinner and a movie with Richard. She gets up and he pulls her back down and kisses her, assuring her that she could stay. She of course gets up to go for real: "Leave you wanting more and all that." Derek is past even looking like he enjoys this pathetic flirting. Her voice-over finishes, "But when you're talking about human chemistry, only one thing matters. Either you've got it, or you don't." Cristina punctuates the statement by slowly beginning to paint a wall in her apartment red.
At the Summer Camp for Lovelorn Surgeons, the Chief drops off a pile of clothes on the table where Derek is enjoying the paper. He announces that this is his dry cleaning, and that there's a stain on one sleeve that Derek should make sure they note. Derek furrows his brow like the pro he is, but the Chief just happily forges ahead with plans for the evening. "I'm thinking Godfather tonight." Derek unenthusiastically says that sounds good, and as Richard walks away he does a questionable Brando: "I'm gonna make him an offer he can't refuse." He's very proud of himself, and Derek humors him. As Richard turns to walk back to his trailer he mouths, "Stella!"