Commentary for Kiddushin 56:7

Resh Lakish disagrees with R. Yohanan about what acquires. He holds that money does not acquire, and that even from the Torah only meshikhah acquires. The problem is that if he holds like R. Nahman that produce cannot effect barter, how can he understand the mishnah? So in the end, you have to say that he holds like R. Sheshet, who holds that produce can effect barter. So he can interpret the mishnah in the following manner quoted from above: “And produce too can effect a barter. How so? If one barters the meat of ox for a cow, or the meat of donkey for an ox, as soon as one party takes possession, the other assumes liability for what is given in exchange.”