The only thing we love more than seeing our favorite characters on TV is seeing the actors who portray those characters ... LOSE it. Actors (just like the rest of us) tend to make mistakes. But lucky for us, when THEY do it, the cameras are usually rolling.
Check out these great gag reels from 24 of our favorite sci-fi TV series. (And since no actor likes blowing a line, be warned there'll be occasional NSFW language.)