At the football game, every time the home team scores a touchdown, the person behind you blasts an air horn near your ears causing you to wince. Unfortunately for you, the home team scores frequently. As the end of the game nears, the home team scores a touchdown, and even though the inconsiderate fan behind you has left, you still wince.

The blast of the air horn is an unconditioned stimulus.

Explanation:

The passage is a description of unconditioned stimulus, a term found in classical conditioning. Unconditioned stimulus is one that triggers a response, a reaction, naturally, automatically. When someone right behind your blasts an air horn, your natural, automatic reaction is to wince, as anyone would when surprised by a loud noise. However, in the situation described, the unconditioned stimulus that is the blasting of the air horn has become associated with the team scoring. Now, every time the team scores, you wince, even though there is no one blasting the air horn any longer.

good question. i'll be looking into that. (this is a joke sir)