(Mishnah): If Reuven and Shimon were partners in a pit, and Reuven [used it] and did not cover it, and Shimon [used it] and did not cover it, Shimon is liable.

If Reuven covered the pit, and Shimon came and uncovered it, he is liable;

If Reuven covered the pit, and Shimon found it uncovered and did not cover it, Shimon is liable;

If one properly covered a pit and an ox or donkey fell in and died, he is exempt;

If he covered it improperly and an ox or donkey fell in and died, he is liable.

If an animal fell forwards, due to the noise of the digging, he (the owner of the pit) is liable. If it fell backwards, due to the noise of the digging, he is exempt.

If an ox fell in with its Kelim and they broke, or a donkey with its Kelim and they tore, he is liable for the animals and exempt for the Kelim.

If fell in a Shor Cheresh, lunatic or Katan, he is liable;

[If fell in] a son or daughter, male or female slave, he is exempt.

(Gemara) Question: How can there be a pit of partners? [If one is liable only for a pit in Reshus ha'Rabim, one cannot sell it or be a Shali'ach to make it!]

Answer (R. Yanai): The case is, both of them put the last rock [at the top, which completes the Shi'ur of 10 Tefachim above the floor of the pit - MAR'EH HA'PANIM].

Question: Why didn't he say that Reuven dug 10 [Tefachim] and Shimon dug 10 [more]?

Answer: He wanted to resolve how we find a pit of 10 Tefachim of two partners.