How did the animal rationalize the executions of the other animals?

Once the terror abates, some of the animals recall the Sixth Commandment, “No animal shall kill any other animal.” Clover again asks Muriel to read to her from the wall, only to find that the Sixth Commandment has been changed to: “No animal shall kill any other animal without cause” (98). Clover and Muriel convince themselves that the commandment has always been that way and decide that treachery justifies murder after all.