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?

  Options: 
 A. A cat sees a mouse and crouches.
 B. A parrot hears a name and repeats it.
 C. A person eats spoiled food and vomits.
 D. A worm senses water and moves to the surface.
Answer: C