Jill likes candy. If Jill asks for candy during the afternoon then her mother will say "No, it will spoil your supper." Jill discovered the following trick.  She asked for candy while her mom was on the phone.  She discovered that if her mom is on the phone talking to a friend, she will say "OK, you can have a piece. Just go away and don't bother me now." So now Jill waits until her mom is on the phone and then she asks for candy because it works. The mom comes to rely on this method to get Jill to stop bothering her.

Take Jill's perspective.  If the response is Jill asking for candy when her mom is on the phone, then Skinner would label the effect: