Derek: When has Mark Sloan allowed his interns to do anything, let alone harvest a bone graft?
Meredith: He's in the race for Chief. He's trying to prove that he can teach.
Derek: By teaching you. Your mother died and the Chief is going to be watching you very closely. Mark is trying to gain points by...
Meredith: Using me.
Derek: If it goes well, then he gets the credit but if it goes poorly, then he gets the save.
Meredith: So this is about you one upping Mark?
Derek: He's using you. I'm just trying to protect you.
Meredith: You don't have to. Close the door on your way out.