Fillion was fielding questions at the St. Louis Comic-Con's Firefly panel when one particularly saucy questioner asked him about his history with Guardians director James Gunn. Fillion starred in Gunn's breakout movie Slither, and wore a ridiculous costume as The Holy Avenger in Super. Given his relationship with Gunn and Avengers 2 director Joss Whedon, this fan asked Fillion, "Were you wanting to get a part in Guardians of the Galaxy?"
Fillion, mischievous devil that he is, responded, "Wanting to? Or maybe, did?" After the crowd calmed down he continued, cryptically, "I'm just sayin' maybe. Maybe there'll be a surprise. Maybe check the credits after the movie when you watch it." At which point the entire auditorium went bananas. The fun starts at the 38:22 mark in the YouTube video below.