1. Rav: One is not allowed to learn anything (Rashi: even a Torah thought) from a heretic.
2. Rav: In certain circumstances, one is allowed to learn witchcraft from a sorcerer.
3. The Gemara extols the person who understands the meaning of the movement of the sun, stars, and constellations.
4. Rabanan: Threshing on Shabbos applies only to items that grow from the ground.
5. Rav: One who slaughters an animal may be liable for the Melachah of slaughtering and for the Melachah of coloring.
A BIT MORE
1. The Gemara proves this from Rav's usage of the word "Magosh" in his statement that a "Magosh" or "Amgusha" means a heretic (in contrast to Shmuel's view that it means a sorcerer).
2. If a sage needs to defend himself from witchcraft or he needs to ascertain whether a prophet who seems to be performing miracles is a false prophet because he is using witchcraft, he is allowed to learn witchcraft.
3. The Gemara scorns a person who can understand these things but does not study them, and it says that it is a Mitzvah to study them and understand them.
4. This explains why one who squeezes the blood out of a Chilazon is liable for hunting, but is not liable for threshing. Since a Chilazon is a living creature and does not grow from the ground, the Melachah of threshing does not apply to it.
5. He is liable for coloring if he wants the blood to remain on the neck of the animal to show that it is fresh, in order to entice customers to buy it from him.