Nedarim 43 - Vagaries of vows
If A is prohibited by a vow to receive any benefit from B, and then A does not have what to eat, what is B to do if he wants to feed A? B can go to a storekeeper whom he frequents and tell him, "A does not have what to eat, and I don't know what to do about it." The storekeeper can take the hint and feed A, and B can then repay him. This is allowed since B never explicitly promised to repay, so the storekeeper acts on his own accord.
If they were traveling together on the road and A does not have what to eat, B can give food as a present to other travelers, and they can feed A. If there is no traveler with them, B can put the food on a rock and say, "This food is ownerless, and anyone can take it," and A can then eat it.
Rabbi Yose does not allow B to feed A by putting food on a rock, because it is obvious that he is giving food as a gift. Some say that even giving through other travelers is not permitted by Rabbi Yose.
Art: Feeding Time by V. Chevilliard