Commentary for Kiddushin 56:4

This is an entire reinterpretation of the mishnah such that the mishnah does not teach that produce or animals can effect barter. My explanation follows Rashi. The beginning of the mishnah states that money can sometimes be used to acquire through barter, even though the money was given as such and not as a form of barter. If Reuven sold Shimon an ox for a man, and Shimon drew the animal to him, he is now liable to give the maneh to Reuven. Reuven now says “Give me the cow instead of the money.” Shimon says yes. If Shimon says, “I am giving you this cow in place of the money” Reuven acquires the cow without having to pull it towards himself. We have now avoided the problem of produce effecting barter.