Mutuable connective tissue can be made rigid or flexible., depending on the voluntary response to circumstances faced by a particular animal. The degree of change in the rigidity of mutable connective tissue is almost as great as that of ice to water. Indeed, people who have firsthand experience of echinoderm tissues passing from rigid to flexible states, liken the transition to liquification. A softening of the connective tissue is made use of by brittle star, many of which will readily cast off an arm in response to being seized by a potential predator. In this case, a rapid depolymerization occurs at a break point , and the arm literally falls off. A similar, local softening of connective tissue occurs in sea cucumber , enanling them to forcibly eject parts of their viscera (evisceration) or parts of their body wall in response to predators and other factors. Hardening of the connective tissue also has a functional importance. For example, sea urchins normally wave their spines about, but when some species enter rocky crevices for protection, they elevate and lock their spines, wedging themselves in the crevice. The spines lock in place because the flexible connective tissue ligaments at the base of each spine polymerize and become rigid. Although relatively flexible, starfish also can stiffen their body by a similar mechanism. For example, while attempting to feed on a clam, the starfish dermis stiffens and the body becomes a rigid scaffold from which the tube feet extend and pull on the clam’s valves.