Of all the animals, man is the only one that is cruel. He is the only one that inflicts pain for the pleasure of doing it.

Arguments to the effect that it is wrong to cause pain and suffering to animals are often rejected by claiming that animals simply do not suffer. … Ironically, it is precisely upon the assumption that animals do suffer from stress, fear, and pain in a manner similar to humans that the validity of much of animal experimentation rests. Few, if any, conditions are studied as widely in animals as are pain, stress, ulcers, fear, and anxiety.

No animal suffers worse than a human being.

Humans — who enslave, castrate, experiment on, and fillet other animals — have had an understandable penchant for pretending animals do not feel pain. A sharp distinction between humans and 'animals' is essential if we are to bend them to our will, make them work for us, wear them, eat them — without any disquieting tinges of guilt or regret. It is unseemly of us, who often behave so unfeelingly toward other animals, to contend that only humans can suffer. The behavior of other animals renders such pretensions specious. They are just too much like us.

God has given to Man an absolute right to take the lives of other animals, for any reasonable cause, such as the supply of food; but He has not given to Man the right to inflict pain, unless where necessary.

Men are the only animals that devote themselves, day in and day out, to making one another unhappy. It is an art like any other. Its virtuosi are called altruists.

The violence of beast on beast is read As natural law, but upright man Seeks his divinity by inflicting pain.

He could not think of the animals without shuddering in anguish. He looked into the eyes of the beasts and saw there a soul like his own, a soul which could not speak; but the eyes cried for it: "What have I done to you? Why do you hurt me?" He could not bear to see the most ordinary sights that he had seen hundreds of times—a calf crying in a wicker pen, with its big, protruding eyes, with their bluish whites and pink lids, and white lashes, its curly white tufts on its forehead, its purple snout, its knock-kneed legs:—a lamb being carried by a peasant with its four legs tied together, hanging head down, trying to hold its head up, moaning like a child, bleating and lolling its gray tongue:—fowls huddled together in a basket:—the distant squeals of a pig being bled to death:—a fish being cleaned on the kitchen-table.... The nameless tortures which men inflict on such innocent creatures made his heart ache. Grant animals a ray of reason, imagine what a frightful nightmare the world is to them: a dream of cold-blooded men, blind and deaf, cutting their throats, slitting them open, gutting them, cutting them into pieces, cooking them alive, sometimes laughing at them and their contortions as they writhe in agony. Is there anything more atrocious among the cannibals of Africa? To a man whose mind is free there is something even more intolerable in the sufferings of animals than in the sufferings of men. For with the latter it is at least admitted that suffering is evil and that the man who causes it is a criminal. But thousands of animals are uselessly butchered every day without a shadow of remorse. If any man were to refer to it, he would be thought ridiculous.—And that is the unpardonable crime. That alone is the justification of all that men may suffer.

There are probably no creatures that require more the protective Divine word against the presumption of man than the animals, which, like man, have sensations and instincts, but whose body and powers are nevertheless subservient to man. In relation to them man so easily forgets that injured animal muscle twitches just like human muscle, that the maltreated nerves of an animal sicken like human nerves, that the animal being is just as sensitive to cuts, blows and beating as man. Thus man becomes the torturer of the animal soul, which has been subjected to him only for the fulfilment of humane and wise purposes; sometimes out of self-interest, at other times in order to satisfy a whim, sometimes out of thoughtlessness—yes, even for the satisfaction of crude satanic desire.

He said that man’s heart was the only bad heart in the animal kingdom; that man was the only animal capable of feeling malice, envy, vindictiveness, revengefulness, hatred, selfishness, the only animal that loves drunkenness, almost the only animal that could endure personal uncleanliness and a filthy habitation, the sole animal in whom was fully developed the base instinct called patriotism, the sole animal that robs, persecutes, oppresses and kills members of his own tribe, the sole animal that steals and enslaves the members of any tribe.

To a man whose mind is free there is something even more intolerable in the sufferings of animals than in the sufferings of man. For with the latter it is at least admitted that suffering is evil and that the man who causes it is a criminal. But thousands of animals are uselessly butchered every day without a shadow of remorse. If any man were to refer to it, he would be thought ridiculous. And that is the unpardonable crime.

"People speak sometimes about the "bestial" cruelty of man, but that is terribly unjust and offensive to beasts, no animal could ever be so cruel as a man, so artfully, so artistically cruel."

Wild animals never kill for sport. Man is the only one to whom the torture and death of his fellow-creatures is amusing in itself.

We find amongst animals, as amongst men, power of feeling pleasure, power of feeling pain; we see them moved by love and by hate; we see them feeling terror and attraction; we recognize in them powers of sensation closely akin to our own, and while we transcend them immensely in intellect, yet, in mere passional characteristics our natures and the animals' are closely allied. We know that when they feel terror, that terror means suffering. We know that when a wound is inflicted, that wound means pain to them. We know that threats bring to them suffering; they have a feeling of shrinking, of fear, of absence of friendly relations, and at once we begin to see that in our relations to the animal kingdom a duty arises which all thoughtful and compassionate minds should recognize - the duty that because we are stronger in mind than the animals, we are or ought to be their guardians and helpers, not their tyrants and oppressors, and we have no right to cause them suffering and terror merely for the gratification of the palate, merely for an added luxury to our own lives.