This is a quote from the book "Animal Farm" by George Orwell
...

The birds did not understand Snowball’s long words, but they accepted his explanation, and all the humbler animals set to work to learn the new maxim by heart. FOUR LEGS GOOD, TWO LEGS BAD, was ins cribed on the end wall of the barn, above the Seven Commandments and in bigger letters. When they had once got it by heart, the sheep developed a great liking for this maxim, and often as they lay in the field they would all start bleating “Four legs good, two legs bad! Four legs good, two legs bad!” and keep it up for hours on end, never growing tired of it.

...
read full book block explorer