The New Yorker writes about W. Reginald Bray, a legendary prankster who, more than one hundred years ago, tested the limits of the British postal system. I’m not sure whether today you could get away with mailing a stamp-covered skull:
Bray was an avid collector who amassed stamps, postmarks, train tickets, and girlfriends, and who, after reading the entire British Post Office Guide, impishly determined to take the rules as challenges. He tried posting an unimaginable array of things, to see whether the post office would deliver them. Apparently, at the time, the smallest item that could be posted was a bee, and the largest an elephant. Bray seems to have tried most things in between. At one point or another, he mailed a bowler hat, a rabbit skull (the address spelled out on the nasal bone, and the stamps pasted to the back), a purse, a slipper, a clothes brush, seaweed, shirt collars, a penny, a turnip (address and message carved into the durable tuber), an Irish Terrier, and a pipe, among other curios.