I took me a minute to realize what I was looking at - very funny! I can't imagine meeting the challenge better than this. Wish the image held my interest more though, in some way. I'm not sure what it is, sorry ... possibly if there weren't such a tight crop on either side vertically? I really don't know. But I do think it's a really clever take on the challenge. Good imagination!
I see you took the challenge quite literally. A cage with no animal, therefore no subject. A nice take on the challenge although the image itself is a bit lackluster.