Dwarf Fortress simulates a whole fortress, down to what's spilled on the floor. When Tarn Adams added taverns to fortress mode, the cats started getting drunk and throwing up all over the tavern. He explained why to PC Gamer in 2016, and it took four rules that were never written together.

One: dwarves get mugs and drink, and mugs get spilled, so there's alcohol on the floor. Two: old code, written so blood leaves footprints, now puts any liquid a creature walks through on its feet. Three: cats lick themselves clean, and licking swallows what it cleans off. Four: that counted as a full dose, a whole mug of alcohol for a cat-sized body. In his words: "they all got drunk. Because they were drinking."

The tavern, the dwarves, the cats and the dose picture in this film are our own simplified version, built in code; every rule is Tarn Adams' own description. Not affiliated with or endorsed by Bay 12 Games or Kitfox Games.

Which game's strangest bug should we cut open next?

Sources: Tarn Adams to Wes Fenlon, "How cats get drunk in Dwarf Fortress", PC Gamer, 31 March 2016.
Sounds: our own, made in code.