1.A person's 'Dalet Amos' in a 'Simta' can be used to be 'koneh' for him anything found, bought, or received as a gift. But is it big enough to be 'koneh' an elephant? If it is; of what use are the 4 'Keylim' that R' Zeira needs?!
2.R' Zeira requires 4 vessels in a 'Simta'; wherein the elephant places his feet; to acquire the animal. This is in order that the airspace above the vessels should be considered to belong only to the buyer. But how is the buyer 'koneh' the rest of the parts of the elephant, say the head and the tail, which are not in the air space above the vessels?! And why do you need 4 vessels?
Kol Tuv
alex lebovits, toronto, canada
1. Tosfos (DH "Beheimah Gasah") explains in the name of Rabeinu Chaim Kohen that the normal selling process is that a seller brings his animal to a certain place, and is then approached by a buyer who proceeds to acquire it. Being that the "Dalet Amos" of a Simta are determined by whoever is next to a space in the Simta first, the animal is presently standing in the seller's part of the Simta. This is why the buyer cannot acquire it using Simta, and why Rebbi Zeira requires the vessels. [We do say that his vessels can acquire in a Simta even when the seller "claimed" the Simta first, as they both agree to this Kinyan and it is only a Simta (see Meiri at the end of 25b).
2. The Meiri says "now all of the animal is in his vessel." This means that being that the only things supporting this animal are the vessels, it is considered as if the entire animal is "in" his vessel.
Kol Tuv,
Yaakov Montrose