Learning the hard way

A hungry flatworm in my jelly and amphipod aquarium tank approaches a jelly resting on the wall:

"Mmmm . . . This looks tasty! And no hard shell to worry about!"

"Yikes! It's got stingers!"

And he backs off, in a hurry, somewhat rumpled around the edges.

He rested a few inches away the rest of the afternoon before he made another approach, with the same result. Then he hurried off to hunt something safer, even if it does have a hard shell; his boring, everyday diet of barnacles and mussels.