Units of Measurement

I'm just beginning to catch up on what happened over chol hamoed Pesach (last week) so you'll have to bear with me a bit.
Playing in the yard on Friday morning, Tirtze found a dead rabbit behind the forsythia. Either some predator got scared off before finishing its meal, or some fox is really, really bad at creating food caches. Anyhow, Jeffrey wasn't sure whether he should just bag the carcass and put it in the municipal trash for collection, so he called animal control. They told him they only got involved when a county resident finds a carcass "bigger than an adult opossum."
Somehow using an adult opossum as a unit of measurement just really amuses me. You know, "smaller than a breadbox, bigger than an adult opossum."

Maybe I'm just sad and easily amused. It reminds me of Dave Barry though, who once wrote about how when wildlife writers discuss piranha attacks, they always use cows as a unit of measurement, a la "a school of piranha can skeletonize a cow in 5 minutes!" He wanted to know why a cow was a standard unit of measurement. Do cows frequent piranha infested waters? Do piranha often prey on cows?