The Bears “butt plug” (also known as “Tappen” or “Rectal Plug“) is made out of dense feces. In the past it was thought that bears got themselves ready for hibernation by consuming large amounts of indigestible plants and thus form a rectal plug that prevented them from eating. This was proven wrong but still being mentioned in the media due to lack of knowledge.

Wildlife Researchers from Minnesota found that most of the plug is intestinal secretions and cells that form during hibernation, which means that the plug actually forms in the intestine mostly during the several months of the hibernation period, the feces just stays there so long that the walls of the intestine suck all its fluids and making the plug dry and hard, the leaves and “indigestible plants” turned out to be all sorts of stuff that bear intake while grooming and licking their fur.

So… Why do they have this butt plug? Well, no one is entirely sure, it could help prevent bugs or ants from entering during hibernation, it could help to prevent defecation during hibernation, or maybe both.

Source>> Wikipedia – Tappen (biology)