Answer:
The improperly refrigerated potato salad at his family reunion
Explanation:
Unconditioned stimulus: In psychology, the term "unconditioned stimulus" is described as a specific stimulus that is automatically, unconditionally, and naturally triggering a particular response.
Example: When an individual smells a food that he or she likes to eat, then he or she may feel hungry immediately, however, in this scenario the unconditioned stimulus is considered as the food's smell.
In the question above, the unconditioned stimulus is the improperly refrigerated potato salad at his family reunion.