Perhaps his favorite thing to do is to jump up in my lap and climb onto my desk to see if there's anything interesting he can steal. If he jumps back down quickly, I know he found something. Usually it's a water bottle cap or a note I left laying.
The other day I had been using my sewing machine and I had to change the bobbin. Instead of putting the other bobbin away I left it sit. You guessed it, Gibbs found it. I heard a crunching noise and when I turned around I see a thread sticking out of his mouth. He was not about to give it up. I had to bribe him with a treat to trade me for the bobbin.