Museum accession # x1963 42 01
- It's a bison hairball. What? That thing was in an animal?
Yes, in fact, much like hairballs in cats, hairballs in bison can be created by licking their own and other bisons’ fur. Unlike feline hairballs, bison hairballs can become trapped in the gastrointestinal tract and oftentimes a shell is formed around them. Technically called 'bezoars', these balls develop around not only masses of fur but also antler tines, twigs, gravel, bullets, pebbles – potentially any foreign object that isn’t expelled from the body.
The term ‘bezoar’ purportedly derives from the Persian words for ‘protection from poison’, and bezoars were once treasured - particularly by royalty afraid of poisoning by opponents - for this specific medicinal property. “It is said that a gold-framed specimen was included in the 1622 inventory of Queen Elizabeth I’s crown jewels.”
|Example of bezoar pendant that could be dipped in a drinking cup for poison testing.|
Netherlands, ca. 1600-1650. bezoar and gold filigree, 11cm.
BK-NM-7082 Rijksmuseum, Amsterdam.
Image used with permission.
Bison and other ruminants, such as cows and oxen, can carry bezoars because of the unique anatomy and physiology of their four-compartmented stomachs. Anything swallowed makes its way to the first compartment - the rumen. From the rumen, food is regurgitated as ‘cud’ for rumination. The cud is swallowed and then travels to the reticulum.  “Bezoars are frequently found in the rumen and reticulum and are formed through the rolling movements of these two forestomachs during rumination.” This mass remains lodged in the animal, potentially causing digestive problems or life-threatening situations “if obstruction of the esophagus, cardia, pylorus, or intestinal tract occurs.” 
|"University of Minnesota Extension --Dairy", University of Minnesota, Accessed July 22, 2016.|
Used with permission.
In the case of the museum’s four inch wide and four inch high bison bezoar, openings in the outside layer allow us to see the "matted, compacted brown hair inside". One can see the rock-like formation surrounding the hairball. In an email several years ago, Dan Sharps, former biologist at the National Bison Range in Moiese, Montana, stated that whatever is at the core of a bison bezoar is “coated with minerals present in the animal’s diet in an attempt to protect the animal from harm” and this shell is described as a calculus or concretion. One wonders how long this particular heavy-looking and obtrusive bezoar was carried around by the animal.