Kevin McKidd

Grey's Anatomy star Kevin McKidd steps behind the camera this week to direct an episode, which he says is "one of the scariest things I've ever done in my life."

Thursday's episode will include the launch of Derek's Alzheimer's clinical trial, Bailey tweeting from the operating room, and the beginning of parenthood for Mark, Callie and Arizona. How did his directorial debut go over? McKidd dishes:

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Worst (Exhausted) Direction: "There were a couple moments where I had to direct Sara Ramirez and Sandra Oh, and I basically gave them bad direction," he says. "It had been a long day and I was trying to squeeze the last bit of something out of myself. I had given them a straight-ahead corny, cheesy direction. I said, 'Be more sad,' which is one of the worst directions you can give to an actor. They both called me out. They both raised their eyebrows, like, 'Really? I'm not going to do that.'"

Biggest Challenge: "In general, the episode is very static. A lot of the scenes took place in a room with people just talking and no movement," McKidd says. "So I worked hard to try and relocate a lot of the scenes that didn't necessarily need to be in a patient room or an O.R. Whether it was them moving, or an exterior, or the cafeteria, I was trying to get the life of the hospital going again."

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Most Emotional Scene: "It's the first day of Derek's Alzheimer's clinical trial. There's a very emotional scene between a husband and wife, and the impact of Alzheimer's on a marriage. One of my grandparents had Alzheimer's and another one had dementia, so it's been in my family. It was quite hard to revisit that, but I think it helped me help the actors get to a place where they really gave amazing performances."

Easiest Actor to Direct: "Eric Dane is amazing," McKidd gushes. "He came up to me and said, 'Just tell me what you want me to do. I've learned the lines. You just tell me what you want me to do and I'll do it.' And he did. I've never had an actor say that to me before. Usually actors are fighting and saying, 'No, I want to do this!'"

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Easiest Scene to Direct: Since McKidd was on director duty, Owen is very light in this week's episode. "Shonda Rhimes made him go to the dentist for the day," McKidd says. "I do one scene. Actually, getting to act in that one scene was the thing that really made me settle into directing. Getting to go back to what I know, which is acting, made me suddenly just sink into it and go, 'Oh, this isn't as strange as it actually seems.'"

The McKidd-directed episode airs Thursday at 9/8c on ABC.