A toxin produced by a marine snail contains a variety of proteins, and injecting one of them into a mouse will put two-week-old or younger mice to sleep, leaving older mice in hiding. When a serious threat occurs, the response of the very small rats is to stay asleep, while the larger rats escape. Which of the following hypotheses is most strongly supported by the facts stated above? ['Very small mice are likely to be as vulnerable to sudden and serious threats as larger mice.', 'The main function of the protein contained in the snail toxin injected into the mouse body is to protect the snail by inducing the snail to completely rest.', 'Adult mice can also fall asleep if injected in large doses.', "The rat's response to a sudden and serious threat is stimulated by a chemical produced in the body, which is similar to the protein injected into the mouse."]