Christmas crackers are festive table decorations that make a snapping sound when pulled opened, and often contain a small gift and a joke. They are part of Christmas celebrations in the United Kingdom, Ireland, and Commonwealth countries such as Australia (where they are sometimes known as bon-bons), Canada, New Zealand and South Africa.
A cracker consists of a segmented cardboard tube wrapped in a brightly decorated twist of paper with a prize in the middle, making it resemble an oversized sweet-wrapper. The cracker is pulled apart by two people, each holding an outer chamber, causing the cracker to split unevenly and leaving one person holding the central chamber and prize. The split is accompanied by a mild bang or snapping sound produced by the effect of friction on a shock-sensitive, chemically impregnated card strip (similar to that used in a cap gun). One chemical used for the friction strip is silver fulminate.
Crackers are typically pulled at the Christmas dinner table or at parties. In one version of the cracker tradition, the person with the larger portion of cracker empties the contents from the tube and keeps them. In another, each person has their own cracker and keeps its contents regardless of whose end they were in. Typically these contents are a coloured paper hat, a small toy, a small plastic model or other trinket, and a motto, a joke, a riddle or piece of trivia on a small strip of paper. The paper hats, with the appearance of crowns, are usually worn when eating Christmas dinner. The tradition of wearing festive hats is believed to date back to Roman times and the Saturnalia celebrations, which also involved decorative headgear.
Christmas crackers are also associated with Knut's parties, held in Sweden at the end of the Christmas season.
Tradition tells of how Tom Smith of London invented crackers in 1847. He created the crackers as a development of his bon-bon sweets, which he sold in a twist of paper (the origins of the traditional sweet-wrapper). As sales of bon-bons slumped, Smith began to come up with new promotional ideas. His first tactic was to insert love messages into the wrappers of the sweets (similar to fortune cookies).
Smith added the "crackle" element when he heard the crackle of a log he had just put on a fire. The size of the paper wrapper had to be increased to incorporate the banger mechanism, and the sweet itself was eventually dropped, to be replaced by a trinket: fans, jewellery and other substantial items. The new product was initially marketed as the Cosaque (French for Cossack), but the onomatopoeic "cracker" soon became the commonly used name, as rival varieties came on the market.
The other elements of the modern cracker—the gifts, paper hats and varied designs—were all introduced by Tom Smith's son, Walter Smith, to differentiate his product from the rival cracker manufacturers which had suddenly sprung up.
Tom Smith merged with Caley Crackers in 1953.
A Christmas cracker is the subject of The Party Favor, an oil painting by American artist Norman Rockwell.  The painting appeared as cover art for The Saturday Evening Post on 26 April 1919.
Passengers on commercial flights in and to the United States are explicitly prohibited from carrying Christmas crackers on board or in checked baggage.  In the United Kingdom, rules vary by airline and airport.
Media related to Christmas crackers at Wikimedia Commons