In an attempt to scare children into good behavior around Christmas, some parents would often tell their kids that Santa would fill their stockings with coal instead of presents on Christmas morning if they were naughty. And since the kids already knew that Santa knew just about everything, this strategy sometimes worked and the parents got a couple weeks of good behavior in winter. At least, it would work until the kids realized that their parents were putting them on about Santa delivering coal. To get back at your kids for less-than-perfect behavior this holiday season (not that we're implying that they're anything less than angelic!), you could actually give them some coal - Coal Gum. The box has 2.5 ounces of sweet, but black, gum.
In Italy, where the coal-in-stockings legend got started, parents can give their kids Carbone Dolce, or "sweet coal" as a treat on Christmas. It is basically a mixture of chocolate and puffed rice cereal that is melted together and left to harden into lumps of "coal."