A sheretz was found dry in an alley. When does it create retroactive impurity?
Halacha 4 (ch. 18): a dry sheretz imparts retroactive impurity to everyone who passed through until the last time the alley was confirmed clean. If it was swept (without checking) it goes back before the sweeping.
Question 2
A container with a rim (handle) was used to fill 10 barrels of water. A sheretz is found in one barrel. What is impure?
Halacha 1 (ch. 17): if the drawing container has a rim, it is possible the sheretz was in the rim, fell out during filling, and contaminated all barrels. Therefore all barrels are impure.
Question 3
Olives were brought from a pit to a roof. A mound of olives formed on the roof 4 days later, and a sheretz was found inside the mound. Is the pit impure?
Halacha 6 (ch. 17): if the sheretz was found in a mound on the roof more than three days after the olives were transferred, the pit is pure. Within three days, we would assume the mound came from the pit.
Question 4
A seed from an impure food is found inside a hot cooked dish. Is the dish impure?
Halacha 9 (ch. 17): when an impure food's seed is found in hot food or inside a loaf, we presume the entire impure food fell there and dissolved — making the food impure.
Question 5
Blood was found on a terumah loaf. The Sages investigated and ruled the loaf pure. What was their reasoning?
Halacha 11 (ch. 17): even if one says the blood is from a sheretz, one can also say it was from a living sheretz — and the blood of a living sheretz is pure. Therefore the loaf is pure.