"Among these, animals are classified as the one of the three (or four) unfortunate rebirth destinies ... The category of animals includes both land and sea creatures, as well as insects. The specific kinds of suffering that animals undergo are frequently mentioned in Buddhist texts; these include the constant need to search for their own food while always seeking to avoid becoming food for others. ... The possibility of achieving rebirth out of the realm of animals is said to be particularly difficult because of either the inevitable killing in which predators engage or because of animals' constant fear of becoming prey; neither mental state is conducive to higher rebirth."