Having already prohibited blood in Pasuk 16, why does the Torah repeat it here?
Rashi" To incorporate in the Isur, Dam ha'Tamtzis 1 - the blood that flows after the initial blood (the Dam ha'Nefesh) has finished spurting out.
Ramban #1 (in Pasuk 22): To teach us that, although it is compared to a Tzvi and an Ayal, its blood does not require covering, as the Pasuk concludes.
Ramban #2 (in Pasuk 22): To teach us that in spite of the concern that people may sacrifice to demons - which is why the blood of Chayos and birds requires covering, the Isur of eating it overrides this concern. 2
Seforno: 'Make sure that the blood is not fit to drink, by pouring it out on the ground and not storing it like one stores wine, oil and other liquids'.
What are the ramifications of the Torah's comparison of blood to water that is poured out?
Pesachim, 22a #1 (according to R. Avahu) 1 : It comes to permit blood be'Hana'ah, like water that is poured out.
Pesachim 22b #2 (according to Chizkiyah) 2 : It comes to preclude Dam Kodshim from being Machshir seeds for Tum'ah.
Why does the Torah insert the (otherwise superfluous) phrase "Al ha'Aretz Tishpe'chenah ka'Mayim"?
