This is a molted, clipped wing feather. There is only one currently left on His Majesty, The Great Green Wonder, aka Peanut, The Master Of The Universe.

Aka The One Wot Flies To The Top Of The Finsterium.

He's such a naughty boy. For a while I was herding him down with a big spoon, saying "Go home!" loudly, and telling him what a good boy he is when he gets there. It's all about encouraging the good behavior, right? But in this case, it isn't working very well. Because he's just lost that next-to-last clipped wing feather, and he likes it on top of the Finsterium, and I'm afraid that even when I get his feathers clipped, he'll still be able to get up there. After all, if he can fly from his house to the top of my head while I'm sitting on the couch with his wings clipped, he can probably fly from his house to the top of the Finsterium with his wings clipped. Sure, there's more lift required, but less distance. I'm afraid that the cat is already out of the bag, as they say.

(Have you noticed how many sayings involve cats? What's with that?)

Since herding Peanut off the top of the Finsterium isn't stopping him from doing it, I've tried another plan, which is to distract him. Instead of making a big fuss when I get him down, I do it quickly and quietly, and then do something else with him. You know, play a game with him, distract him with a drink of water from a new container, walk briefly into the bedroom while he's on my head.

Here's an impromptu play gym that kept him occupied for about three minutes: