Pets I didn't know I had.
It's a dead mouse. In the picture you can see its skull, a hind leg, its spine curving, and trailing away into a long mousy tail, and, uh... it kinda looks like it's been dead for a while now. Likely a year, or more. It's been a while since I've been this deep into the big ol' pile o' boxes. Amazingly, there's no blood, no flesh, and no strong smell either. This mouse is just bones and dust now.
Along with the mouse I found a whole bunch of little capsule-like objects. I think these are discarded puparia, left over from when the maggots graduated into their adult, fly, stage. The one I'm picking up with the tweezers, the one I wanted my camera to focus on, is out of focus, but the others, on the rug, are sharp and easy to see.
These various creatures lived out their lives in a not-often-visited corner of my house, without me really being aware they were there, and it made me think that the distinction between the inside of my house, where I live, and the outside of the house, where nature and wild animals live... well, it's kind of an artificial distinction, because clearly there are wild animals living in my basement!
Anyway, probably the sane way to look at this is not as a nature documentary, but as a warning not to let too much junk pile up inside your house.