Have you ever heard of a Madstone? It’s a bit of old deer lore I was reminded of recently.
Madstones, also called bezoars, beazlestones, or enteroliths, form in much the same way as pearls in shellfish (due to their rarity, some deer experts consider them even more valuable). A foreign body, such as a coin, hairball, or even a clump of dirt, remains in the stomach rather than passing through the intestines. Over time, mineral salts (particularly phosphates) and food particles coat the object.

Bezoars come in several different types. The madstone-type is usually smooth and rounded like a river pebble. Hairballs coated with minerals are called trichobezoars, and may be either soft and stringy or hard and urchin-like. Balls of plant fibers form phytobezoars, and may be either smooth or knotty and rough. A combination of hair and plant fiber may form phytotrichobezoars, which are often soft and velvety. Size-wise, bezoars can run from smaller than a pea to nearly twenty pounds. Bezoars are often found in the stomachs or throats of horses, occasionally found in ruminants such as deer, cattle, or goats, and rarely seen in cats, dogs, and even humans. They don’t present a danger to the animals unless the bezoar blocks the intestine.
Magical power has long been ascribed to these stones. During the Middle Ages, for example, bezoars were thought to cure epilepsy in children, break fevers, prevent plague, cure rabies, and neutralize any poison from snakebite to arsenic (the word bezoar is derived from the Persian word padzahr, which means “expelling poison”). Even in modern times, some people collect the stones for their reputed curative powers or for just plain good luck.
Beazlestones are also found in deerhunter’s lore. Some local traditions say that white or piebald deer carry the stones in their throats, others say that any deer can have them. According to the folktales, a wounded deer coughs up its madstone, bringing good fortune to the hunter that finds the pebble. More likely, the stone is found in the rumen when the deer being dressed. In these times when most deer go through a commercial processor, I expect many madstones are never recovered.
Finding a madstone is a bit of luck in itself. Whether or not they bring good luck is a question I leave to you.
