B'Coz they r only interested in their bodily needs in the existence on this earth.What is an animal interested in?Food,sleep and sexual satisfaction.When a man is interested only these,he is lyk b an animal.Bible says god created us his in own image n his lykness(conciousness upright,with character and self control,and not a slave to animal practices).The fact that we are clever than the animals and better than them!But Even educated ppl are slaves to greedy,sexual lust,anger etc.There is a part of us that is deeper than our minds,and that is our concious that makes us aware of god.This is not animals has.God has made us as moral beings and gave free will that could choose whether obey good(liberty) r bad(bondage).Conscience is gods voice within us that we are responsible for our answers.Oneday we will have to give an answer to god for the way we have lived our lives.