How are dogs trained

In Pavlov's groundbreaking study, dogs learned that a stimulus (in this case, a bell) meant they were about to be fed. Starting with two things that are naturally paired -- salivating and being fed -- Pavlov added a third component by ringing a bell before feeding. After a few trials, the dogs learned to associate the bell with being fed and would react by salivating at the sound of the bell in anticipation of their food but without any food present.