A flash mob is defined as a large public gathering at which people perform an unusual or seemingly random act and then disperse.
JWs are now in on the act and were doing this in Bath on unsuspecting Convention Delegates during their tours after the convention. They did this on at least three seperate occassions.
https://www.youtube.com/watch?v=3HmrqR-K4HQ
Here's another one, not so public though