(Mishnah): If one tells his friend 'I stole, borrowed or received a deposit from you, and I do not know whether I returned to you', he must pay;

However, if he is unsure whether or not he stole, received a deposit or borrowed, he is exempt.

(Gemara - R. Yochanan): [Our Mishnah discusses] one who comes to be Yotzei Yedei Shamayim. (There was no claim against him.)

If one tells his friend 'I stole, borrowed or received a deposit from you, and I returned to you', and the other says 'I do not know', R. Yirmeyah wanted to say that he must pay according to letter of the law;

R. Yosi wanted to say that also here [he must pay only] to be Yotzei Yedei Shamayim.

[If he says] 'I took out of the wallet and gave to you [what I owed you]', and he says 'I do not know', Rav Huna says, we tell him, you do not remember. He remembers (he is exempt even bi'Ydei Shamayim. We explained this like MAHARA FULDA.)

(Mishnah): If one stole a lamb and returned it to the flock, and it died or was stolen, he is liable;

If the owner did not know about its theft or return, and counted the flock and found that it was complete, he is exempt.

(Gemara - R. Yochanan): If the owner knew about its theft, he must know about its return [for the thief to be exempt; the Reisha discusses this]. If he did not know about its theft, he need not know about its return (as long as he counted and found that the flock is complete).

(Reish Lakish): Even if he did not know about its theft, he must know about its return (unlike R. Yochanan said, that in this case counting suffices. The Seifa teaches that counting suffices, i.e. when he knew about its theft, which the Reisha discussed.)

(R. Lazar): If [the theft] was like this goat, he need not [count the flock or] know about its return.

Question: What does it mean 'like this goat'?

Note: In Bava Basra, it says that Mesirah of Mashchunis is like Mesirah of the entire flock. Our Gemara brings the three opinions about what is Mashchunis, and the last one answers the question here.

Answer #1: It is a staff (the flock sees it, and follows it).

Answer #2: It is a bell (the flock follows it).

Answer #3: It is a big male goat (it goats at the head of the flock, and the others follow it).