R. Yosi (in Demai) and Rabban Shimon ben Gamliel (in our Mishnah) both have the same opinion. (The Mishnah in Demai 3:5 teaches that if a person gave flour to an innkeeper's wife to prepare dough, he must separate before he gives her and after he receives it back, as she is suspected of switching it. R. Yosi disagrees and says that we are not responsible for swindlers - he must only separate from what he takes back from her.) Both R. Yosi and Rabban Shimon ben Gamliel said that we are not responsible for swindlers.

It's logical to say that R. Yosi would agree with Rabban Shimon but Rabban Shimon would not agree with R. Yosi. R. Yosi would agree to Rabban Shimon that we are not responsible for swindlers; but Rabban Shimon would not agree with R. Yosi, as it's not normal for a Chaver to give out something that is not tithed.

Question: What's the source for labelling graves?

Source #1 (R. Berachia bar R. Yaakov bar Bas Yaakov citing R. Chunia of Beras Chavran, and R. Yosi said it was R. Yaakov bar Acha citing R. Chanania of Beras Chavran and R. Yechezkel said it was R. Uziel son of R. Chuna of Beras Chavran citing his father: The pasuk states (Vayikra 13:45), "...and (the Metzora) shall call out 'Tamei' 'Tamei'" - so that the Tumah calls out to you and says, "Stay away".

Source #2 (R. Hila citing R. Shmuel b'R. Nachman): The pasuk states (Yechezkel 39:15), "And those that pass in the land will pass by and see a human bone, they shall build next to it a sign". This teaches that we label bones. 'Human' - this shows that we label spines and skulls. 'And they shall build' - this teaches that we label on a fixed stone; as if it would not be fixed, it could roll elsewhere and cause Tumah to other things. 'Next to it' - this teaches that it is fixed near, but not on the Tumah. 'A sign' - this teaches that a sign must be made.

(Tosefta): If a person found a single labelled stone, even though one stone shouldn't be labelled, if one passes over it, he is Tamei, as there assumedly is a corpse underneath it.

If there were two, if one passed over them, he is Tahor; if between them he is Tamei.

If he plowed between them, each stone is viewed as a single stone - between them is Tahor; around the plowed area (i.e. the place of the stones) is Tamei.

(Tosefta): One should not label flesh, lest it decompose (and one might come to declare items Tamei unnecessarily).

Question (R. Yustai bar Shunam to R. Mana): (If you don't label) perhaps items will become Tamei until the flesh decomposes?

Answer (R. Mana to R. Yustai): It's better to have temporary damage than permanent damage.

(Chevraya): (The Mishnah taught (Erchin 2(b)) that R. Shimon ben Gamliel said - When is it (that we label Revai and Orlah)? In Sheviis (when all produce is Hefker and anyone may enter a person's field to take it); but in other years (when the person entering is intending to steal), 'Feed it to the wicked man and let him die'.) Rabban Shimon ben Gamliel spoke well, so why do Chachamim disagree, requiring labelling in all years? The label only helps in the daytime, but since the thief comes at night (when the label is not visible), how does it help?

Answer (R. Mana to Chevraya): (Since the thief comes) in the daytime to mark for himself the place where he will come back to steal later on, he will see the label.

Support (R. Chanina): The pasuk states (Iyov 24:16), "In the dark, he digs under houses; by day, they lock themselves in; they see no light." 'By day, they lock themselves in' - this was the behavior of the generation of the flood - they would deposit strong smelling balsam oil with rich people. The rich people would put it in their hidden storerooms. At night, the people would come back and find the riches in the storerooms by smelling the oil.

When R. Chanina expounded this in Tziporin, three hundred tunnels of thieves were dug.