The animals are amazed and horrified to see Squealer, then other pigs, walking upright, but once again the bleating of the sheep forestalls any protest. How has their slogan changed?

They changed to "4 legs good, 2 legs better"

Explanation:

This question refers to the book "Animal Farm" where animals, tired of being exploited by human beings, start a revolution to expel humans from the farm where they live and regulate anything that refers to humanity, assuming that everything that walks on two legs and bad.

However, once oppressed, pigs begin to be oppressors and establish a dictatorial system in which they are abusive towards other animals. The pigs are so similar to the human behavior that they criticized so much that they started walking on two hind legs, as erect as the man, they claimed that "4 legs good, 2 legs better".