Give an example of an unconditioned stimulus.

An unconditioned stimulus (US) is a stimulus that naturally and automatically triggers a response without any prior learning. In other words, it is a stimulus that elicits a reflexive or innate response without the need for conditioning. An example of an unconditioned stimulus is the smell of food, which naturally causes salivation in most animals, including humans. This response does not need to be learned; it occurs naturally. In the context of classical conditioning experiments, the famous example given by Ivan Pavlov involves the use of meat powder as an unconditioned stimulus, which elicited an unconditioned response (salivation) in dogs.