Cue Balls

Have you ever wondered how a coin-operated pool table is able to differentiate the cue ball from the others? I did, and I found out how:

Coin-operated pool tables such as those found at bars and college campuses historically have often used either a larger ("grapefruit") or denser ("rock", typically ceramic) cue ball, such that its extra weight makes it easy for the cue ball return mechanism to separate it from object balls (which are captured until the game ends and the table is paid again for another game) so that the cue ball can be returned for further play, should it be accidentally pocketed. (www.wikipedia.com)

Interesting isn't it?