Growth on our community mailbox

I spotted this today, not often I go around the back of our mailbox. Nature does it again!  I think it's a kind of moss, and the leaf that landed on it and got caught is a definite bonus.
In my crazy imagination, I see that leaf riding a two-headed dog, one head on either end, with a belly dragging on the ground. The leaf reminds me of a bull rider leaning way back with legs in the air and both arms outstretched.