If one dug a pit 10 Tefachim, and another plastered it and decorated it, both of them are liable.

Question: Because he plastered it and decorated it, he is liable?!

Answer #1: The case is, [the owner] said "plaster this pit and acquire it'';

(R. Ami citing R. Lazar): Meshichah for damages is like Meshichah for Kinyan. (If one acquired something, he is obligated to guard it.)

Answer #2 (R. Simon): The case is, he dug in sand. (Had the latter not plastered it, the walls would have collapsed and it would not be deep. We explained the answers like HAGAHOS R. DINAR; also NESIVOS YERUSHALAYIM explains Answer #2 like this);

(Beraisa): If this one dug 10 Tefachim, and this one dug 10; this [one dug] 20, and this 20; this 100 and this 100, all of them are liable.