chucklebones

An infestation, these little thumb-sized critters appear like tiny many-armed, sharp-toothed gremlins which when folded up, disguise themselves as a set of bone gambling dice. If fed properly, they can be trained to weight themselves in the user's favor, and to sneak around the board, checking cards and stealing coins. Rogues and charlatans will often have a set of these on hand in a pouch, as they also work as a sort of pickpocketing and lock-picking tool. The little creatures are extremely mischievous, however, and prone to flashes of temper. They will often conspire against their owner to play pranks upon them or nip at their fingers if not treated fairly.
If the infestation grows large enough, they may demand gold as payment for their services. Chucklebones colonies have been known to appoint a "queen" which will make itself known by sinking its teeth into your finger and refusing to enter the pouch with the other dice when you try to put them away for the night. It will not let go until you offer it a gold piece or something of equivalent worth. You will need to offer some of your winnings each time you gamble with your chucklebones from that moment onward.
The bigger a gambler their owner is, the greedier the band of chucklebones will become. Thus, the gambler will tend to gamble further to keep up with both their own addiction and the hunger of the chucklebones.
To detect chucklebones during a game of dice: try making a good pun, casting a detect-evil-and-good spell (they are minor fey species) or sprinkle the table with breadcrumbs, which they can rarely resist. Listen carefully, and you may hear quiet, high-pitched giggling coming from the tabletop.
To expel an infestation of chucklebones from your person, you may need to cleanse yourself of gambling habits, keeping them out of use. Once you stop feeding them, they will undoubtedly jump to the next willing host at the next tavern. If all else fails, take a bath in holy water blessed by a cleric, or gift your dice pouch to an unsuspecting enemy. :)