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.
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A sneak preview of Grey's Anatomy episode 4.07, "Physical Attraction, Chemical Reaction." Cristina lectures Lexie about not talking about her personal life, when a baby and her mother both arrive in need of urgent care.
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A short ABC promo for "Physical Attraction, Chemical Reaction," the seventh episode of Season Four of Grey's Anatomy. Looks like a lot to keep track of in this one!
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Grey's Anatomy Season 4 Episode 7 Quotes

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.

Derek: What's new with you?
Meredith: I saw my half-sister half naked.