Pavlov's dogs

     People often refer to Pavlov's dogs, but the reference is somewhat vague to anyone who hasn't studied some psychology. Pavlov, working about 100 years ago, was investigating what is called "conditioned response".  He rang a bell every time he fed his now-famous dogs. The dogs learned (were conditioned) that the bell meant that they were about to be fed. Eventually, the dogs began to salivate (drool)  as soon as they heard the bell--whether Pavlov fed them or not.  Pavlov proved that autonomic responses--responses that are physical, and over which we have no conscious control, like sweating or drooling--could be influenced by an external stimulus, such as the bell, other than that which would actually produce the response (drooling), such as the food.
     To "salivate like Pavlov's dogs", as the Rolling Stones had it, would be to get all worked up over, say a picture of food, a person, or some other unreal thing that is connected to the response ( getting worked up, feeling hungry)  through one's own memory.