Atticus compares the mob to what?

Atticus compared the mob to "a gang of wild animals" (To Kill a Mockingbird, Chapter 16).  Scout and Jem expressed their concern about the mob the morning after the group confronted Atticus in front of the jail.  They were concerned that the mob members could have hurt or killed Atticus.  Atticus gently dismissed their fears.  He reminded his children that the mob was made up of friends and neighbors from in and around Maycomb.  He told them that "a mob's always made up of people, no matter what."
Scout had a hard time grasping this concept.  She recalled that Mr. Cunningham had been considered a friend of the Finch family.  Despite this, he had at first behaved in a threatening way with the mob.  Atticus reminded Scout that even though Mr. Cunningham was part of the mob, he was still a human being.
Atticus also reminded his children that they had helped disperse the mob.  Scout had spoken to Mr. Cunningham with friendliness.  Atticus tied this in with his belief that mobs are made up of people:

"So it took an eight-year-old child to bring 'em to their senses, didn't it?" said Atticus.  "That proves something—that a gang of wild animals can be stopped, simply because they're still human."