A MOVING SUKAH
Question: Who is the Tana who permits a Sukah on a wagon or boat?
Answer: R. Akiva (and R. Gamliel argues).
The Beraisa reports an incident in which R. Akiva's Sukah blew off the boat.
R. Gamliel asked R. Akiva regarding the whereabouts of his Sukah.
(Abaye): The point of dispute between R. Akiva and R. Gamliel is only regarding a Sukah strong enough to withstand land winds but not strong enough to withstand normal sea winds.
R. Gamliel looks for Mechitzos in a permanent Sukah at its current location (i.e., on the boat).
R. Akiva judges the walls as whether they are Halachically viewed as Mechitzos for a temporary dwelling, an assessment made on land.
A SUKAH ON AN ANIMAL
Question: Who is the Tana who permits such a Sukah?
Answer: R. Meir (and R. Yehudah argues).
Question: What is R. Yehudah's rationale?
Answer: The Pasuk indicates that the Sukah must be a residence for seven days which this Sukah, due to the prohibition of entering it on Yom Tov, does not fulfill.
Question: And what will R. Meir claim?
Answer: Mid'Oraisa, this Sukah is valid for seven days (as the prohibition to go on the animal is mid'Rabanan)!
USING AN ANIMAL AS A SUKAH WALL
(R. Meir): An Sukah is Pesulah if an animal is serving as a wall (R. Yehudah permits it).
(R. Meir): Anything alive may not serve as a Sukah wall, as a Lechi, as posts around a well nor will it receive Tum'ah as the cover on a grave.
(R. Yosi ha'Gelili): Gittin may not be written on it, as well.
Question: What is R. Meir's rationale for prohibiting an animal's use as a Sukah wall?
Answer (Abaye): Lest the animal die.
Answer (R. Zeira): Lest the animal run away.
A case which would illustrate the difference between them is an untied elephant.
Its death would not invalidate the Sukah since it would remain 10 Tefachim.
It might well run away, however.
Question: Surely Abaye should be concerned that the animal may run away!?
Answer: Indeed, and an untied elephant may not be used.
They argue, instead, by a tied smaller animal.
We are concerned for its death (Abaye).
We are not concerned lest it run away (R. Zeira).
Question: Surely R. Zeira should be concerned lest it die!?
Answer: We view death as improbable.
Question: But there is open space under the animal's legs (which would invalidate the Sukah)!?
Answer: We close up the opening with foliage.
Question: But the animal may crouch!?
Answer: It is tied upright with ropes from above.
Question: Such tying should eliminate our concern for its dying, as well (it would still be a Mechitzah even if it died)!?
Answer: If it is exactly the minimum wall when alive (seven Tefachim and a bit, with less than three Tefachim from the Sechach) its death would cause it to shrink, invalidating the Sukah.
VIEWING DEATH AS (IM)PROBABLE
Question: But, unlike the above, Abaye holds that R. Meir is not concerned for death (and R. Yehudah is)!?
There is a contradiction where a Mishnah allows the wife of a Kohen to eat Terumah on the assumption that her husband is alive, and a Beraisa where such a woman must refrain from eating Terumah lest her husband has died.
Abaye resolves the contradiction by saying that the Mishnah is R. Meir who is not concerned about death, and the Beraisa is R. Yehudah, who is.
Abaye supports this distinction by citing a Beraisa regarding the tithing of wine.
R. Yehudah is concerned about the designated barrel breaking (and would certainly be concerned about a person dying).
R. Meir is not concerned about the barrel breaking (and would not be concerned about a person dying).
Answer: We must reverse Abaye's positions of R. Meir and R. Yehudah in the above resolution, to bring his positions in line with 3.b. and c. above.
R. Meir is concerned for death and R. Yehudah is not.
In support of this distinction, Abaye may cite our Beraisa, wherein R. Meir forbids the use of an animal and R. Yehudah permits it.