Mishnà su Levitico 15:2

Rabbi Judah says: there are six instances of lenient rulings by Beth Shammai and stringent rulings by Beth Hillel.The blood of a carcass: Beth Shammai pronounces it clean, And Beth Hillel pronounces it unclean. An egg found in a [bird’s] carcass: if the like of it were sold in the market, it is permitted, and if not, it is forbidden, according to the opinion of Beth Shammai. And Beth Hillel forbids it. But they agree in the case of an egg found in a trefa [bird] that it is forbidden since it had its growth in a forbidden condition. 3+4) The blood of a non-Jewish woman and the blood of purity of a leprous woman: Beth Shammai pronounces clean; And Beth Hillel says: [it is] like her spittle and her urine. One may eat fruits of the seventh year with an expression of thanks and without an expression of thanks [to the owner of the field], according to the opinion of Beth Shammai. But Beth Hillel says: one may not eat with an expression of thanks. Beth Shammai says: a waterskin [is liable to become impure only if it is] tied up and remains unimpaired. And the school of Hillel says: even if it is not tied up.