Below are a pair of memorable scenes from last night's Grey's Anatomy.

First, Mark admits to Derek that he is seeing Lexie, and after the day Derek's been having, he's reached his breaking point. Sloan's admission was the straw that broke the camel's back.

The two come to blows in front of the whole hospital ...

[video url="http://www.tvfanatic.com/videos/the-breaking-point/" title="The Breaking Point"] [/video]

Follow the jump for another memorable scene from "An Honest Mistake," in which a woman confronts Izzie about being misdiagnosed with cancer when she was really just anemic.

The patient is fairly pissed at the error - but it's the other person who is far worse off, she says. Izzie then looks through the files to confirm what she already knew in her heart ...

[video url="http://www.tvfanatic.com/videos/misdiagnosed/" title="Misdiagnosed"] [/video]

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.