There's No Shot Like A mug shot!

Many of you have written in and asked us what a Mug Shot is, scientifically speaking: "Does it have anything to do with mung?" asks T.S., Pasadena. "Why must these people be shot?" wonders P.U., Kalamazoo. "You can't tell a book by looking at its Mug Shot!" insists Worried, Peoria.