What is the meaning of "Lo Sochlu al ha'Dam"?
Rashi #1 and Targum Yonasan 1 : It is a prohibition against eating the meat of Kodshim before the blood has been sprinkled.
Rashi #2: To eat from the flesh of an animal whilst it is still alive. 2
See Peirush Yonasan and Na'ar Yonasan.
Ramban In fact, this seems to have been the sin of King Shau'l's army, cited in Shmuel 1, 14:33, as intimated there in Pasuk 32. Rashi adds that the Gemara in Sanhedrin, 63a, lists many other interpretations of this La'av. The most relevant of them - not to eat before having 'prayed for one's blood' (See Torah Temimah, 202). The Ramban and the Rashbam too, refer to the Gemara in Sanhedrin.
Ramban: in keeping with the other La'avin in the Pasuk. And it entailed gathering blood into a pit, thereby attracting the demons, whom they would then question about the future - and that was the sin of King Shau'l's army, who were terrified of the P'lishrim, whom they were currently fighting. Rashbam: it entailed eating by the grave and performing witchcraft to prevent the deceased from taking revenge, or some other kind of witchcraft.
Seforno: which the Torah forbids because it means departing from the Ru'ach Taharah that surrounds Yisrael to a Ru'ach Tum'ah.
What is the difference between "Lo Senachashu" and "Lo Se'oneinu"?
Rashi: The former is a La'av against superstition - If one comes across a weasel or a bird; 'The bread fell from his mouth!' 'A deer crossed his path!'; the latter, superstition in connection with time - 'Such and such a day is good to start working!', That time of day is bad to go out!'.
Ramban (in Devarim 18:9): The former is witchcraft via the chirping of birds or looking at their wings; the latter, witchcraft visa the formation of the clouds.
Targum Yonasan: It is a prohibition against imitating the Sanhedrin, who study sorcery. 1