Past special interests of his I've personally been around for are:

China/Chinese history
Aztecs/Aztec history
Freshwater fish and aquariums
Domesticated birds and bird training
Flint knapping
Linguistics
War in Ukraine
Court TV/YouTube (Karen Read trial)
Dinosaurs
Geology/rocks/mining for gems?

The deal is: my husband always has a special interest. I've learned a lot over the years but I don't know what to do with the info and.. it can be overwhelming to be given a lecture on random subjects frequently/unexpectedly. So, I figured I'd start this account to pass on the knowledge.