I hate to ask… But would that even feel good for the sponge? Would that even feel like anything? From what we can see, there’s nothing in there. The starfish’s fingers aren’t stimulating anything; they’re just waggling in the air inside the sponge. Beyond simply the stretching of the hole, I can’t see the sponge really getting anything out of this act. And the most I can see it doing for the starfish is providing a convenient carry handle for his friend.