This bizarre expression is phrased around a situation where there is something embarrassing to hide. Its origins go back to the 1830s when it was illegal to dissect human bodies, so grave-robbers and murderers supplied medical schools and doctors with bodies. These had to be hidden in case of raids. William Makepeace Thackeray, a renowned British novelist, author and satirical writer of Vanity Fair, used this phrase for the first time in print in the year 1845.