Grey's Anatomy The real test to determine whether an actor is doing an effective job is not just how well he or she acts in a scene but how he or she re-acts. We had some really great reacting tonight. An obvious example is

Sandra Oh's facial expressions as Cristina was forced to be Bailey's baby-sitter. How hilarious was she while changing the baby's diaper? Then when she told the baby to "Shut it!", I had to TiVo back and watch it again. But back to the reacting. Patrick Dempsey's face said it all while Meredith was explaining to Derek the horrible thing she did to George. Meredith asked Derek to act like a friend, not as her ex, and you could tell he was struggling just by the expression on his face. I love that he told Meredith to apologize to George in the elevator. Then T.R. Knight gave my favorite reacting performance of the night as Meredith apologized to George you could tell just how mortified and hurt he was. And what a perfect way to end the episode, with Derek apologizing to Addison and Kate Walsh reacting exactly the way we'd want her to. Tonight was chock-full of impressive guest stars. Natalie Cole was unforgettable, in every way (you knew I had to write that). Actually, she really was good. I never thought I'd see Natalie play a woman with a brain aneurysm and a fork in her neck. I'm sure Veronica Mars fans recognized Teddy Dunn as the hockey player who cut his own finger off (ouch). Then there was the fabulous Anne Moore as the very pregnant woman who's husband, played by Stephen Lee, couldn't stop flirting with Addison (and Addison didn't mind the attention). But the best guest star was Jeffrey Dean Morgan, back as Denny, the man capturing Izzie's heart while in need of a new heart of his own.