Nedarim, Chapter Four, Mishnah Eight
This mishnah deals with a situation where Shimon who may not benefit from Reuven, is walking on the road with Reuven and Shimon runs out of food to eat. The question is, how can Reuven give food to Shimon without breaking the vow?
1) If they are walking together on the road, and he has nothing to eat, he can make a gift to a third person, and he is permitted [to eat] it.
2) If there is no one else with them, he may put it on a stone or a wall and say, This is free to whomever desires it, and the other takes and eats it.
a) Rabbi Yose prohibits this.
Section one: In this scenario, there is a third person walking on the road with Reuven and Shimon. Reuven may give the food to the third person, with the assumption that Shimon will take it from him. As long as Reuven does not give the food directly to Shimon, the vow has not been transgressed.
Section two: According to the first opinion, if there is no third person walking with them, Reuven may put the food down and declare it legally ownerless and then Shimon may take it. Although it is obvious that Shimon is going to take the food, and no one has taken possession of it since Reuven had possession, this is still permitted.
Rabbi Yose forbids this, and considers it to be no different than Reuven giving directly to Shimon.