Hurrah! Ten bucks online got me two of these:

Basically, owl hairballs containing everything the they can't turn into nutrients--fur and bones, mostly.

Half an hour's work got me these:

Mouse skulls! Which I then put in a disposable plastic cup full of bleach and water and floor cleaner and ajax (whatever I could find under the sink, really) overnight.

This morning I cleaned them and painted them, and not I have a new earring! Also two other skulls that I'm not sure what to do with, and a cool thing I made by gluing together two jawbones. I don't expect that this earring will last very long (tiny and fragile) so here's documentation: