Behind the scenes: Anderson Cooper surprised by Murray's Santa song

Many of you had the same question about AC360's exclusive jailhouse interview with Michael Jackson's doctor: What was going through Anderson's mind when Dr. Conrad Murray started singing "The Little Boy That Santa Claus Forgot"?

Producer Jack Gray sat down with Anderson to relive the unforgettable live TV moment and ask him on your behalf.

Understand that it's not easy to surprise a globetrotting veteran journalist, but Anderson sure was, confirming it was the first time someone broke into song during an interview. Reflecting on the two-part segment, he says, "it took a very bizarre twist" when Murray switched from explaining to singing about his connection with Jackson.

In the beginning of the interview, Murray's lawyer interrupted to prevent her client from saying anything that could harm his appeal, but she was silent during the song. "I was curious to see if she was going to try to interject to stop the singing," Anderson says. "How would you really do that in a way that didn't come off as odd?"

Watch the video for more of his reaction, and check out part I and II of the full interview with the man who maintains he's not at fault for his patient's fatal overdose.