Blue Butterfly

In the “Blue Butterfly” episode of Castle, Mark played a 1940s club owner/murder suspect, and he says star Nathan Fillion — “a really smart, big kid” — was the source of goofy fun between takes. “At one point he’s like, ‘Hey Mark… So, did you do it? Did you commit the crime?’” (The series star hadn’t yet made it to the end of his script.) “I said, ‘Let me try it and you tell me if you think I did it,’” Pellegrino says, chuckling.

TV Line