The Gemara raises the question of how to deal with a long alleyway that opens to the public domain, but with a series of small alleyways branching off of it on both of its sides, all of which also open to the public domain. To describe such an alleyway, the Gemara refers to it as a “Mavoy He-Asui Ke-Nadal” (an alleyway that is shaped like a centipede). Before we study the Gemara’s discussion, let us spend a moment touching on the Nadal, the creature upon which it is based.
The Nadal is identified as a Scolopendra, one of the multi-legged creatures of the Chilopoda family. All of these creatures have a long body made up of sections, and each section has a pair of legs on either side. The number of pairs differs from one centipede to another. The centipede Scolopendra possesses twenty-one pairs of legs and has a pair of poisonous claws near its head, used to deliver venom into its prey. While painful, their sting is not ordinarily dangerous to human beings. When the Torah (Vayikra 11:42) refers to “Marbei Ragla’im” (many legged creatures), it most likely is referring to these creatures.
There is a difference of opinion among the Rishonim as to how the model Nadal defines the Gemara’s case. According to Rashi, it seems that all of the smaller exits to the public domain are on one side of the Mavoy. Tosafot bring the opinion of Rabbenu Tam, which states that they are on both sides of the Mavoy, but they do not match up. Most Rishonim, however, understand the case to be where the smaller openings are exactly opposite one-another.
The Gemara teaches:
Abaye said: An opening in the form of a doorway is made for the large alleyway, and all the small alleyways are permitted by means of a side post or a cross beam.
Rava said to him: According to whom do you state this halakha? Apparently according to the opinion of Shmuel, who said that the halakha of a crooked L-shaped alleyway is like that of an alleyway that is closed at one side. For in this case of an alleyway that is shaped like a centipede, when each of the smaller alleyways connects to the larger alleyway, it forms a crooked L-shaped alleyway. However, if the halakha is indeed in accordance with the opinion of Shmuel, why is the form of a doorway needed for it? According to Shmuel, an alleyway of this kind only requires a side post or a cross beam at each end in order to permit carrying within it. And furthermore, with regard to the crooked, L-shaped alleyway in Neharde’a, which was Shmuel’s place of residence, didn’t they take into consideration the position of Rav? This indicates that the halakha in practice follows Rav as opposed to Shmuel.
Abaye’s suggestion is that a full doorframe should be built to “close off” the main entrance of the Mavoy, and the smaller openings will suffice with the Lehi (side post) or Korah (cross beam) usually used to permit carrying in the Mavoy.
Rava responds to Abayye by arguing that each of the smaller openings should be considered a Mavoy Akum (crooked alleyway), as each one goes from the public domain on one side to the large Mavoy, which itself leads to the public domain. If you follow Shmuel’s opinion that that Mavoy Akum is considered “closed,” then there should be no need for a doorframe; a Lehi or Kora should suffice. However, we learned above (6b) that in Shmuel’s hometown of Neharde’a, they followed Rav’s ruling that the Mavoy Akum is considered “open.” Rava concludes that we must follow Rav, and therefore all of the smaller openings on one side need to be “closed” with a doorframe, and the other openings can then be symbolically closed by use of the Lehi or Kora as in any standard Mavoy.