Following hyperlinks from topic to topic on Wikipedia as you continually come across concepts you want to explore in more detail. It usually results in simulatenously exploring multiple deep threads of related topics, but ending up in various places far from where you began.
I starting reading about Money Creation on wikipedia, and after wikihopping for an hour ended up reading about famous modern cases of Japanese ritual suicide. True Story.
An act of precautionary racism, crossing the street is undertaken by white men or women when a larger number of young black men are walking towards them on the same side of an otherwise quiet or dark street. While it is becoming more widely recognised that most black men are non-aggressive, it's better to be safe than sorry.
I saw a black man coming towards me while I was wearing my Nikes and listening to my IPod, so thought I'd cross the street early just in case.