What are the weirdest things you've had to research for your story/fic/script?

I've definitely had to research the "usual" things like the finer details of how cyanide works on the body and how much lye it takes to dissolve a body, but my favorite writing rabbit holes have been about things like European bread and ham prices in 1914 and accrate screwdriver terminology.

How about y'all? What kinda rabbit holes have you guys stumbled down for your own writing?