Quicksand is a mixture of mud and water, sometimes with sand, that can kill those walking in it, by sucking them under.
Quicksand is usually caused by water collecting beneath sand or loose earth, more often seen in jungles such as the Oasis of Ahm Shere.
In 1926 A.D, the pilot known as Winston Havelock crashed plane into some dry quicksand in the desert of Egypt. He was already dead (a broken neck during the crash) and his plane sunk under the sandy quicksand, taking his dead body with it.
In 1933 A.D, a group of cultists, led by Baltus Hafez waded through the jungle on an expedition to Ahm Shere, but were ambushed by pygmies that pursued and killed large amounts of the group. A few of the cultists blundered into a puddle of quicksand whilst running from the pygmies. Hafez, rather than helping them, fled for his safety. The pygmies didn't hesitate, however, to run across the quicksand, using the men's heads as steps. The last pygmie crossing hopped across, stomping down with both his feet upon their heads each time, purposefully pushing them under and drowning them.