dock leaves

In Watership down one of the stories of El-ahrairah is told, of El-ahrairah's warren being besiged by Kind Darzin.  No rabbit can go out for silflay, and they are starving.

To try to get help, El-ahrairah and Rabscuttle escape to seek out the Black rabbit of Inle. They find him, in his shadow world warren where there is no food for mortal rabbits, and El-ahrairah pleads for the lives of his warren.
The Black rabbit says he doesn't make bargains, and instead plays a game of bobstones with El-ahrairah, who loses. As payment, the Black rabbit takes El-ahrairah's whiskers and tail.
The next night, El-ahrairah says instead of bobstones, they should tell stories, and the Black rabbit agrees. But the Black rabbit tells a better story, and El-ahrairah loses his ears. Rabscuttle helps his wounded chief rabbit, and fashions ears out of dock leaves. Meanwhile, the Black rabbit's owsla tells them they should go, as other burrows in the warren contain death for mortal rabbits.

El-ahrairah hears this, and sits in one of the deadly burrows to catch the illness to kill his warren's besiegers. He goes to the Black rabbit to tell him how he will help his warren, but the Black rabbit tells him the illness in question is spread by fleas in the rabbits ears, and they will not live on dock leaves. He then tells El-ahrairah to go home, and Rabscuttle helps his wounded and defeated chief back to their warren.. which they find is thriving, with no siege.

They ask for one of the owsla members to tell them what happened, they are told that rabbit died a long time ago, in the fighting long past. They realise the Black rabbit saved the warren, and the price was their time, as no one knows them.