The key to a good Christmas cracker joke is not whether it is funny but whether it can illicit groans around a dinner table, experts say [Getty Images] "How much did Santa's sleigh cost? Nothing, it was on the house." The joke is met by groans that echo through a warehouse in Lambeth, London. We're at a joke-testing session with Talking Tables, a London company that makes supplies for gatherings. Its repertoire includes Christmas crackers.