What effect does Charlie's news about finding a golden ticket have on Grandpa Joe?

When Grandpa Joe hears Charlie burst through the door and announce that he has found a golden ticket, he is at first dubious. But when he sees that the golden ticket is real, a huge grin spreads over Grandpa Joe's face and he leaps out of bed. The narrator states that "this old fellow of ninety-six and a half, who hadn't been out of bed these last twenty years, jumped on to the floor and started doing a dance of victory in his pajamas" (47).