This is the new Sigma "Lens Cap Keeper". An excellent invention, if you put down your lens cap and start walking off he will croak at increasing volume until you return the cap to the lens. I seriously need one of these, I'm on my third lens cap for my 50mm.
Tiny toad sitting on my Sigma 30mm. He kept hopping away and I kept putting him on different things. I think he was pretty pissed off by the end. Hopping mad, you might say.
It took me a few shots to get his eye in focus, but I finally managed it!
This was taken while sitting in a field in Germany on a sunny day drinking Jupiler, which is a pastime I'd thoroughly recommend.