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—Carl Sagan

Longer version of the quote

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.