All over the populated areas of the Legend of Zelda: A Link to the Past you find these chickens.

They don't do much except cluck and run away if you hit them with your sword, so you might get bored and just start hacking away at them. They never run out of health, so you can keep it up for a while, until...

The distressed chicken calls in the cavalry and they swarm the screen! These chickens are invulnerable and dangerous to touch. I just hope you were near a doorway so you can run and hide. If not, the onslaught will stop eventually.

Oh, and this works on the skeleton chickens in the Dark World, too.