Coincidence of Noticing Things, in Action

I usually call this (rightly or wrongly) 'synchronicity'.

It's happened to me several times that I see something very obscure on the Internet or TV that I've never known about before. Then a day or two later, in some unrelated medium like (say) a book, or on the radio, I will see a reference to that very subject.

I first noticed it when I learned about a ranch war in the early 1900s somewhere in the US. The very next day, I was watching TV, and there was an oblique reference to that specific ranch war that would normally have gone right over my head. But having learned about it the day before, I knew exactly what the man was talking about.

I made a post 11 days ago (https://news.ycombinator.com/item?id=24814634) about a wikipeida page regarding things evolving into crabs. Then today I see this youtube video on trending (https://www.youtube.com/watch?v=wvfR3XLXPvw) talking about this very same concept. This is a very niche subject so I am surprised by its relative frequent appearances.

This thing has happened to me before, so I finally decided to look up what its called.