Because sponges cannot move quickly, they need ways to defend against predators other than fleeing. Some sponges have sharp skeleton parts (spicules) that protrude from their bodies and are also shed to make a spiny carpet around them. Chemical defenses are critical for sponges, too. Their bodies contain a range of chemicals that can make them bad-tasting or even poisonous to predators. Some of the chemicals are produced by microscopic organisms (such as bacteria and fungi) that colonize them. Both the sponge and the microbe get something out of such mutualism, with the sponge providing a home and nutrients for the microbe and the microbe working with the sponge to make defensive chemicals. Humans may benefit from this relationship as well, because many chemicals isolated from sponges have anti-cancer and anti-bacterial properties. Scientists are isolating specific chemicals from sponges to create life-saving drugs such as the anti-cancer Ara-C.