I have heard of instances in which the bitumen coatings of mummy cases have softened under certain circumstances and become quite 'tacky.'

The men of their armies who fled from before the face of the valiant servants of my Lord Ashur, crossed over the Euphrates; in boats covered with bitumen skins I crossed the Euphrates after them; I took six of their cities which were below the country of Bisri; I burnt them with fire, and I destroyed and overthrew; and I brought their movables, their wealth, and their valuables to my city of Ashur.