Source: SB 1.3.9

So to become obedient servant and to have no discrimination of sex and food, that means dogs and they are not human beings. And camel, although he is a big animal, he takes pleasure in eating his own blood. How is that? You will find the camels are very fond of eating thorns. So the thorns they eat, and the thorns cut the tongue, and the blood comes out. It makes a taste, and he is thinking that the thorns are very tasteful. That is camel.