I'm not tired!

Yesterday Jesi and Christi went shopping. They had to drive about 20 minutes to the store. They had just started on their way when Jesi let out a huge YYYYYAAAAWWWWWNNNN. Christi said: "Jesi, why don't you close your eyes and take a little nap." "But I'm not tired, mommy," Jess replied. Christi said: "Yes you are. You just went YYYYAAAAWWWWNNNN." "Oh," said Jesi. "That means...YYYYAAAAAIIII WANT A FROSTY!" Where does she get it?