Why does avery say, "that's a fine specimen of a pig—it's no bigger than a white rat"?

Which line from the story of my life by helen keller is an example of a simile? during the whole trip i did not have one fit of temper, there were so many things to keep my mind and fingers busy. i was like that ship before my education began, only i was without compass or sounding-line, and had no way of knowing how near the harbour was. one day, while i was playing with my new doll, miss sullivan put my big rag doll into my lap also, spelled "d-o-l-l" and tried to make me understand that "d-o-l-l" applied to both. child as i was, i at once felt the tenderness and sympathy which endeared dr. bell to so many hearts, as his wonderful achievements enlist their admiration.