How many species are called 'sheretz' for impurity purposes, and what is the minimum measure required?
Halachot 1–2: exactly eight species are designated as sheretzim, and the minimum measure to impart impurity is a lentil-sized portion.
Question 2
The blood of a sheretz — can it combine with the flesh toward the lentil-sized measure?
Halacha 7: the blood of a sheretz counts like its flesh and combines toward the lentil measure only as long as it is connected to the body.
Question 3
Whose hide is treated like flesh (imparting lentil-measure impurity)?
Halacha 8: specifically the hedgehog (anakah), chameleon (koach), lizard (leta'ah), and snail (chomet) have hides treated as flesh. The weasel, mouse, ferret, and mole's hides are pure.
Question 4
A frog and a snake are forbidden to eat. Do they impart sheretz impurity when they die?
Halacha 13 (last halacha): frogs, snakes, scorpions and all other teeming creatures, though forbidden to eat, are completely pure. Only the eight sheretz species impart impurity.
Question 5
If a lentil-sized piece of sheretz shrank and no longer measures a lentil, then later swelled back to the lentil size — what is its status?
Halacha 13: once it shrank below the measure it became pure by Torah law. When it swells back, it only imparts Rabbinic impurity. But if it was originally at the measure and merely fluctuated, Torah-level impurity is retained.