On yesterday’s daf we learned the Mishna that discusses how we establish an animal as being mu’ad, and under what circumstances it reverts to being tam. (A shor mu’ad – an ox that has gored in the past – is one whose owner will pay full damages, while the owner of a shor tam – an ox with no violent history – will pay for only half of the damage that it caused.) Rabbi Yehuda ruled that a shor becomes mu’ad if it gores three days in a row; it reverts to being a tam if it goes three days without goring. Rabbi Me’ir taught that a shor becomes mu’ad after three consecutive acts of goring, and it will be considered tam when a child can pet it without it reacting violently.
Our Gemara brings the opinion of Rabbi Yossi who combines the two opinions. According to Rabbi Yossi a shor becomes mu’ad if it gores three days in a row; it becomes a tam when a child can pet it without it reacting violently.
In conclusion, the Gemara quotes Rav Nahman as saying that he rules like Rabbi Yehuda with regard to mu’ad, since Rabbi Yossi agrees with that position, and like Rabbi Me’ir with regard to tam, since Rabbi Yossi agrees with that position. Rav Nahman explains that he follows Rabbi Yossi’s opinion, “She-nimuko imo.” The expression nimuko imo is unclear. Rashi explains that it means that Rabbi Yossi’s proofs and reasoning are with him, while Rabbeinu Ḥananel explains that he has solid Torah traditions that could be relied upon. Some suggest that the root of the word nimuko is the Hebrew omek (with the loss of the letter ayin) meaning that his reasoning is deep and well-founded, but most believe that its source is Greek, meaning that he is a well-versed sage (some Greek writings use the word as a title for the Sages).