What happened when Waverly ask for a bag of salted plums in "Rules of the Game"?

While she's shopping at the store with her mother one day, Waverly asks for a bag of salted plums. But her mother refuses to buy her one. It's not that she's being cruel or vindictive; she just wants her daughter to exercise self-control, which she believes is a necessary precondition of achieving success in life. Nevertheless, whatever her motives, Mrs. Jong angrily scolds Waverly, telling her that, in future, she should learn to bite her tongue in order to control herself.
Whether or not this is the right approach for a parent to take in such circumstances, it seems to work. The next time Mrs. Jong and Waverly go shopping, Waverly doesn't ask for any plums. This tells Mrs. Jong that her daughter has matured and learned her lesson. As a reward for Waverly's self-control, Mrs. Jong quietly plucks a small bag of plums from the rack and puts it on the counter with the rest of the items she's bought.