Please choose the correct answer to the question: When a dog smells food and begins drooling, it is responding to an external stimulus. Which of these describes a response to an internal stimulus?

Answer1: A cat sees a mouse and crouches. Answer2: A parrot hears a name and repeats it. Answer3: A person eats spoiled food and vomits. Answer4: A worm senses water and moves to the surface.

Answer format: answer1/answer2/answer3/answer4