(Tana Kama): A hole that the water or rodents bored into the lower section of the banks of a river or which appeared there after the earth crumbled by itself, or a pile of stones or of beams where some of them formed an Ohel over others all have the Dinim of Tumas Ohel.

(R. Yehudah): Only a man-made Ohel has the Din of Ohel.

This is learned as a Gezeirah Shavah (the shared word Ohel) from Mishkan.

The Tana Kama understands the extra words Ohel to add more types of Ohalos, including natural ones.

Question: But the Beraisa indicates that, according to R. Yehudah, the backs of oxen (surely not man-made) create an Ohel!?

As one of the many precautions from Tum'ah mentioned regarding drawing water for the Parah Adumah, we learn that the children were brought to the Shiloach on the backs of oxen, with platforms attached upon which the children sat.

This created an Ohel which protected the children from contracting Tum'ah from unknown Tum'ah in the ground beneath them.

R. Yehudah taught that the children were borne on the oxen themselves, without the platforms.

Thus we see that R. Yehudah recognized a natural Ohel!

Answer (R. Dimi citing R. Elazar): R. Yehudah concedes the existence of natural Ohalos when they are large (as seen in the cited Beraisa).

Question: But we find that R. Yehudah objected to the use of the platforms, presumably because this is not a normal way to make an Ohel!?

Answer (Abaye): R. Yehudah did not mean that the platforms were invalid as Ohalos, but that they were not needed since the wide oxen served as Ohalos.

Answer (Rava): R. Yehudah meant that they did not use the platforms because the children were used to them (unafraid) and might look over their edge, exposing themselves to possible Tum'ah (whereas they would stay scared in their seats on the backs of the oxen).

A Beraisa supports Rava in its report of R. Yehudah.

Question: How could R. Yehudah permit sleeping under a bed?

Given its width, it should be an Ohel, just as the platform or the oxen constitute an Ohel!

Yet in our Mishnah it is not an intervening Ohel, while in the Mishnah regarding Parah Adumah it is!

Answer: A bed is made for use above it, thus negating the Ohel status of that which is below it.

Question: But oxen are also for use above them!?

Answer (Ravin citing R. Elazar): The underside of the oxen provides shade and rain-cover for the shepherd.

Question: If that is why it is an Ohel below, then the same can be said of the bed which protects the shoes beneath it!?

Answer (Rava): Rather, oxen are an Ohel below since their backs protect their lower parts (as in the Pasuk).

Alternate Answer: R. Yehudah requires that a Sukah be a fixed dwelling and a bed is a temporary dwelling, which is not Mevatel the fixed dwelling above it (the Sukah).

Question: But R. Shimon also requires a fixed dwelling yet he holds that a temporary dwelling does invalidate at fixed one!?

Answer: Indeed, they are arguing over whether a temporary dwelling invalidates the fixed dwelling above it.

The Beraisa (like the Mishnah) learns the two lessons from the Sichah (conversation) of R. Gamliel.

Question: We typically speak of learning from his words (Devarav) not from his Sichah (conversation)!?

Answer: This teaches us, inter alia, that even the casual conversations of the sages warrant analysis.

(Tana Kama): It is permitted to place Sechach on a bed with three walls of 10 Tefachim.

(R. Yehudah): If the Sukah could not stand independent of the bed it is Pesulah.

Question: What is R. Yehudah's rationale?

Answer: It is a Machlokes (R. Zeira and R. Aba b. Mamel) whether the Pesul is because the bed is not fixed or because the Sukah is being supported by that which is Mekabel Tum'ah.

Question: When will we see a difference between them?

Answer: When a Sukah is built on iron poles (which are fixed, but are Mekabel Tum'ah).

(Abaye): The Pesul of R. Yehudah is only if the Sechach is resting on the bed, but if the beds are serving as the walls of the Sukah, while the Sechach is on Kosher poles, the Sukah is Kesheirah.

Question: Why would such a Sukah be Kesheirah?

Answer: Either because the poles are fixed or because he is not resting the Sechach on that which is Mekabel Tum'ah.