Already prior to the Flood, animals were killed to provide clothing for man and for sacrificial purposes. (Ge 3:21; 4:4) However, not until after the Deluge did Noah and his family receive permission from Jehovah to add flesh to their diet, with the stipulation that it must be drained of its blood. (Ge 9:3, 4) While this made it proper for man to kill animals for necessary food, he was not authorized thereby to indulge in needless slaughter for the sheer thrill of the hunt or to display personal prowess, as Nimrod, the rebel against God, undoubtedly did.​—Ge 10:9.

Clean and Unclean Animals. A classification of animals is to be noted in God’s instructions to Noah to take with him into the ark seven of each clean animal and two of each unclean animal. (Ge 7:2, 3, 8, 9) Since a flesh diet had not yet been authorized, this distinction between clean and unclean was probably determined on the basis of what was acceptable to Jehovah as a sacrifice. Hence, on emerging from the ark, Noah knew which creatures were clean and suitable for offering upon the altar. (Ge 8:20) At that time no restriction existed with respect to the type of animals that Noah and his family could eat, as is indicated by Jehovah’s words: “Every moving animal that is alive may serve as food for you.”​—Ge 9:3.