(R. Yosa): I heard here (about this law) from R. Shmuel bar Rav Yitzchak, and I do not know what it is.

R. Ze'ira: Perhaps it is the following. Initially, [the Parshah] discussed only a Tam. It returned [to mention] a Mu'ad for Kofer. It returned [to obligate] both of them for damage;

One might have thought that when it returned [even a Tam] for damage, it returned it also for Demei Eved! "U'Va'al ha'Shor Naki'' exempts from Demei Eved.

(R. La): Everywhere, you are more stringent about a slave than anything else. Even a leper [a useless slave worth nothing, a Mu'ad] pays 30 Sela'im for him. (This is because he is his master's property. Likewise,) I would say that even a father and mother [should be paid for a fetus aborted due to an ox]! It says "u'Va'al ha'Shor Naki'' - from Demei Vlados.