Quicksand is a non-Newtonian fluid : when undisturbed it often appears to be solid ( `` gel '' form ) , but a minor ( less than 1 % ) change in the stress on the quicksand will cause a sudden decrease in its viscosity ( `` sol '' form ) . Quicksand is a non-Newtonian fluid : when undisturbed , it often appears to be solid ( `` gel '' form ) , but a minor ( less than 1 % ) change in the stress on the quicksand will cause a sudden decrease in its viscosity ( `` sol '' form ) .