A plug of indigestible materials that forms in a bear's anus during hibernation.
From the Swedish/Norwegian, tapp-en, 'the plug'.
That cork is stuck in that wine bottle tighter than a tappen in a bear's behind.
And now it's possible that you all hate me for that mental image. You are welcome. There are many theories as to why a tappen forms, including that it prevents insects from entering the bear's digestive tract or prevents the bear from defecating and attracting scavengers or predators. Apparently passing the tappen post-hibernation is quite painful, although I am unsure as to how we know this. Most useless word ever, woo hoo!