I get to the Banshee and realize I've never found a beehive. So, I check my alchemy recipes and sure enough, I've got everything I need to mix a potion of deafness.

I drink it, nothing happens. I don't think about this too hard and attack the banshee and I'm dead.

I look up potions of deafness and I must have mixed a blessed one, which CURES deafness. Lovely.