Probably one of the best examples of how the prisoners were treated like animals (and there were many) was when the prisoners traveled in the cattle cars. They were literally treated like cattle. Elie uses words like "herded" to describe the way that they were loaded onto the cars. The trains would stop periodically to unload the dead without thought of who they were, just as if they were unloading the carcasses of animals. The soldiers would throw food into the cars and they would leave buckets of water in the cars as well and the soldiers left it to the prisoners to fight for it all.
Elie witnessed a son murder his father for a crust of bread and then two other men murder the son for the same crust of bread. He described the scene like these men were reduced to pure animal instinct where hunger and survival superseded relationships and social graces.