The Price of Rice in China and the Price of Potatos in Idah

A few years ago when we had gone to Grandma and Grandpa's house, Grandpa was reading the newspaper like he always does in the living room. I had gone in to talk to him. I had asked what section he was reading and he was reading the commodities section. I had asked him what the price of rice was in China. He pretended to know what the answer was and told me. Ever since then whenever I see him or talk to him on the phone I ask him what the price of rice is in China. He would always tell me that he didn't know the price of rice in China was but that he knows the price of potatos in Idaho are and we would have a conversation on that topic for awhile. So whenever I call to talk to Grandma and Grandpa and I ask those questions right away, he automatically knows that it is me calling to talk to him.