A cat sees a mouse and crouches. A parrot hears a name and repeats it. A person eats spoiled food and vomits. A worm senses water and moves to the surface.
I am hesitating between 4 options to answer the following question, which option should I choose?
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?
Possibilities:
- A cat sees a mouse and crouches.
- A parrot hears a name and repeats it.
- A person eats spoiled food and vomits.
- A worm senses water and moves to the surface.

A person eats spoiled food and vomits.