A taste aversion can develop after a single exposure while most other examples of classical conditioning require many exposures.
Classical conditioning involves the pairing of a previously neutral stimulus with an unconditioned stimulus (US) which produces an unconditioned response (UR). After many pairings, the previously neutral stimulus will elicit the response. Once this happens, the neutral stimulus is called a conditioned stimulus (CS) and the response it produces is the conditioned response (CR). The response remains the same and only becomes a conditioned response when it occurs in the presence of the conditioned stimulus AND the absence of the unconditioned stimulus.
An example of a taste aversion could include eating broccoli (the US) which causes you to vomit (the UR). Typically, before consuming any food item, you smell it or hear the name of it spoken. These could become conditioned stimuli if simply smelling broccoli causes you to vomit. (Or if hearing someone say “broccoli” causes you to vomit.) In this example, the vomit response would be a conditioned response and the conditioned stimulus is the smell of broccoli. The important thing to remember is that taste aversions can develop after a single pairing of the US with the CS. Another key difference is that taste aversions are less resistant to extinction.
Extinction with regard to classical conditioning involves presenting the CS in the absence of the US many times until the CS no longer elicits the CR. To continue with the example above, this would mean you would have to smell broccoli many times until the smell alone no longer elicits vomiting. For taste aversions, this can take many more exposures before extinction occurs than it would for other examples of classical conditioning.