There's a RAT gnawing at my brain!
Thanks, guys, for coming up with the correct identification, just in time to provide the correct caption for this:
(The funny border is due to the fact that I composited two MI images, using a larger-scale but out-of-focus image to fill in a little extra detail around the perimeter.)
For the record, here's the PanCam color composite:
(already 100%)