What are two effects that Rosie had on the characters in the novel?

Rosie the elephant is so central to the novel that she is as much a character as the humans are. She has especially strong effects on Jacob and August.
Jacob, who treats Rosie and the other animals, has the most opportunity to learn from her; in fact, they learn together. August, who is impatient and insensitive, does not manage to learn much from her. Unfortunately for him, he does not believe she has anything valuable to impart. The direct effect she has on him is death because he could not learn the consequences of his bad behavior. More generally, it is clear that Sara Gruen wants the reader to understand the value of the knowledge that animals possess and the ways it resembles human intelligence.
Jacob studied veterinary science in college, but working with Rosie is his first opportunity to interact with such a large, intelligent mammal. He begins the relationship with a solid grounding in the physical care of animals, which aids him in caring for the physical wounds that August inflicts with the hook.
Jacob, in this early stage, has relatively little understanding of animals’s mental processes. However, his personality is well-suited toward caring for the captive animals, as he is a kind and generous person. He can also see how much it bothers Rosie when August mistreats her. By observing her in the first parade in which she appears, he also learns that she is smart; this is confirmed when they all learn that she can pull up her stake so she can get lemonade. He later learns she understands Polish.
August’s understanding of the human to animal relationship is totally one of dominance; in that respect, his attitude toward humans is not that different, as evidenced by the way he treats Marlena. His behavior endangers others, as when Marlena begins to ride Rosie and August scares the elephant so she runs away and knocks off her rider. Rosie becomes August’s scapegoat; he takes out his frustration on her every time things are not going his way, using the hook or hitting her with his cane.
Although Rosie does not respond well to that treatment, August is incapable of changing his methods. When she gets the opportunity, she attacks and kills August using the metal stake she pulls out of the ground.