How quickly those "Watch Lists" can expand

For those concerned about "watch lists" to prevent people from selling guns, it is informative to see how quickly other watch lists can be expanded:

The no-fly list created by U.S. authorities, which singles out passengers who are potential terrorist threats, is the target of frequent criticism that it's incomplete and unreliable. But that hasn't stopped it from expanding dramatically. Aviation sources say the list has grown to more than 31,000, up from 19,000 last September.