You can take one of these guys and put 'em thru a grinder and then pass the ground-up sponge thru a fine-mesh nylon screen and then dump the mess back in sea water. In not so long a time, the teensy pieces will not just clump back together into a whole sponge again, but clump back into it's original shape. That makes scientist's wonder if a piece of your finger knows it's a piece of your finger and knows where it's located on your body.
That's a pretty good trick. Now if only I could think of a way to get them to go on tour...