1. Most of the actors auditioned for different roles than they were given.

Isaiah Washington, or Dr. Burke, auditioned to play Derek Shepherd, not Dr. Burke. Sandra Oh, or Christina Yang, auditioned for the role of Dr. Bailey. Similarly, Alex Karev wasn't even in the original script. They had to add him in after the pilot was shot.

2. Patrick Dempsey and Ellen Pompeo didn’t know Derek’s character was married for a long time. 

Dempsey found out about Addison Montgomery mid-season one, and Pompeo found out at the end of season one. It was a shock to both of them in real life, as well as to Meredith in the show!

3. They use real organs and surgeons for surgeries.

Well, the organs usually come from cows, but they are real! And the medical producer brings in real surgeons for surgeries so that everything you see on the show is as realistic as possible. Some of these things actually happen during real surgeries!

4. Justin Chambers, or Dr. Karev, had five kids and a wife of ten years when the show first started.    

Is this why Karev was so good with kids and somehow always found his way back to pediatrics? It couldn't hurt.

5. Isaiah Washington (Dr. Burke) was fired from the show.

When Burke left the show, it was a shock to Dr. Yang and audiences everywhere. But, it was not his choice. Washington used a homophobic slur toward T.K. Knight (George O'Malley), and was fired from Grey's.