http://psychology.about.com/od/uindex/g/uncondstim.htm
http://psychology.about.com/od/cindex/g/condresp.htm
1.)Art goes to a meeting in New Orleans and tries some oysters at the oysters bar. He likes the taste and eats quite few. Soon he becomes very ill with an upset stomach. Now, even the thought of oysters makes him nauseous.
http://psychology.about.com/od/cindex/g/condresp.htm
The conditioned stimulus (CS) in this example would be the thought of oysters. This is because, after the initial experience of eating oysters and getting sick, just the thought of oysters now triggers a response from Art.
The conditioned response (CR) in this example is Art feeling nauseous when he thinks about oysters. It is a learned response that has been associated with the conditioned stimulus (the thought of oysters) due to the previous pairing with the unconditioned stimulus (eating oysters and becoming ill).