I once saw a group of ranchers butcher a cow in the plains of Paraguay. They had an area of the farm where the cows were slaughtered -- the area was a small patch of grass under a large tree. As the ranchers brought a cow near the tree and tied its tether to it, the cow started shaking and making strange sounds -- sounds you wouldn't expect from a cow. She knew she was about to be slaughtered. The shaking got worse and the cow eventually defecated and peed itself. As the rancher pulled out his knife, the cow started aggressively pulling on the tether and started howling. The cow knew it was going to die. That brief moment left quite an impression on me.