Let me set a quick scene for you ...
You're wandering around your house, minding your own business when all of a sudden, you are scooped up and shoved into a carrier with your sister. You get into a strange smelling contraption that makes odd noises and even worse, MOVES without you making it do so. Then, you are carried into a strange place with even more odd smells and sounds and left there, away from the place and people you trust to care for you. Someone comes in and shaves your belly and then sticks an ouchy needle in your arm. Before long, you feel groggy and things go all hazy. You are frightened but instinct tells you to be quiet and draw as little attention to yourself as possible. Then you are placed on a cold, metal table with VERY bright lights and all of a sudden, you know nothing more until you wake up confined in a cage with no familiar items or companions, and your belly hurts but you don't know why. You stay this way overnight in the strange place. Then you go back home to the people and things you know, but this experience has confused and frightened you. You lash out at anything and everything especially your sister because she smells like the place where they made your belly hurt.