classical conditioning

My mother stays with me from Wed to Sat every week. When Ian comes home from school, he will usually call out "Nai Nai" (grandma in mandarin) cheerfully even before he enters the house. Very often, my mum will "reward" him with a sweet.

Last week, Ian did not behave the same. He came home from school but did not address my mum at all. When my mum asked him for the reasons, he said (showing his palm) "I got sweets already."

Very bad classical conditioning for a child.