It probably wasn't their poop (though I guess that's possible too) but rather their vomit. As I recall, they can't fully digest the bones and fur, etc of their little mousy victims so they throw it up after they digest the meaty bits.
Ha, we did this in elementary school. I have never heard anyone else comment on doing this until you. Must be a pretty rare science class thing
Aha interesting, I thought this was standard for some reason
It is
We actually collected our own from a local park that had a family of owls.
if i remember right we had ours brought in from some park, as we were in a semi-suburban area.