I was watching a Dirty Jobs episode where host Mike Rowe assisted a Bat Biologist into a cave to take temperature readings.

I was rather intrigued when Mike Rowe was trapped in what resembled quicksand but was actually  layers of guano… bat droppings…

I guess this would work similar to quicksand since quicksand is not necessarily sand but any fine granular matter and in this case the bat guano fit the bill.