In January 1997 I lived in Lincoln Park on the north side of Chicago. Here is the story of how I received the head of a cow in the mail.
Listen to the audio here.
Thanks to sir_zman for hosting the audio, even though this audio clip is not suitable for or relevant to his podcast.
This incident foreshadows my interest in opening up boxes to find treasures hidden inside. I don't think the gc.com guidelines explicitly forbid heads of cows in caches, but I'm sure it would be frowned upon.
One part of this story I didn't tell: after the ex-roommates moved away, their dog Cheeto ran away from home and showed up on my back porch to live with me. Now, if I was a much more evil person than I already am, maybe my ex-roommates would have received a little surprise in the mail!