A good way to mark key cards in a deck. Aces, for example, so that you can always spot them quickly in a ribbon spread. If you're into gambling routines, this is an inexpensive way to familiarize yourself with this classic method. For what it's worth, the majority of hustlers over the years haven't been mechanics. They've been paper players. David Malek's Juice decks are also excellent, even though some have complained that it's hard to read the marks. (Which is the point, of course.) For those wanting the work to be especially heavy, all you'll need is "Juice" and a Q-tip. (And good health insurance, should you dare to cross the line.)