"It's nothing til you don't got one."

For those of you who have been following along, Nathan Fillion has finally revealed (Twittered) what the 'Firefly' easter egg was on Monday's episode of 'Castle':

1. How did the catalyzer come to my possesion? I got it the same way Mal would. I stole it.about 15 hours ago from Tweetie
2. Look closely, when Mal comes out the door- under the gun, under the boat, just to the right. It's a nothin' part, till ya need one.about 15 hours ago from Tweetie
3. It looks like @andreajean915 found the Easter Egg. Haven't checked everyone's guess but she's the first. It was... the CATALYZER. BSTL.

You can read more about the catalyzer here and here. Man, you can find just about anything on this here internet, cantcha?

Oh, and there is NO WAY I would have ever found it!