5 Things You Didn't Know About 'Dr. Horrible's Sing-Along Blog'
Nathan Fillion, who worked with Joss Whedon on both 'Buffy the Vampire Slayer' and Firefly', accepted the part of Captain Hammer before knowing what it was. According to the actor, he saw Whedon's name on his caller ID, picked up the phone and said "Yes!" because he knew whatever Whedon was calling to talk to him about, his answer was going to be the same.