It isn't "MEOW", its "ME-NOW" (listen closely). They make this sound to tell humans that they are losing their patience with them. Their best attention getter is a strategically placed (or timed) hairball. Always remember, cats are our overlords (all hail their greatness). That's why they strut around with their tails in the air, proudly displaying their butts. It's they're way of saying, "what you see is what you are to us".