What does Genesis 9:3 mean?

These first verses of Genesis 9 echo God's blessings and commands to Adam, but with certain changes. As He did with Adam, God tells Noah and his sons to be fruitful and multiply and fill the earth (Genesis 9:1). Instead of simply commanding them to subdue the earth, God describes humanity's adversarial relationship with the animals. In this man-dominated relationship, animal-kind would fear people and people will triumph (Genesis 9:2).

God had said to Adam that he could eat from every plant, except for a single forbidden trees. God again gives humanity specific permission to eat, saying to Noah and his sons that they can eat anything that moves, as well as any of the plants. This, in part, might explain the reason why man's relationship with animals is characterized in this passage as hostile.

At this point in God's relationship with humankind, no restriction is mentioned about defining certain animals as edible or inedible: clean or unclean. This may have been understood, in the sense that Noah would have considered those animals not previously defined as "clean" as inappropriate to eat (Genesis 7). The other possibility is that humans may have been free to eat animals categorized as "unclean" until God made them off-limits for His people in the Law (Leviticus 11, Deuteronomy 14).

The permission to eat anything that moves may have included an implied restriction against eating animals which had died of natural causes. In other words, only animals "moving" when man decided to eat them were acceptable.