George Wilson: I can't stand that kid, he's a menace.
Mrs. Martha Wilson: Weren't you a fat boy?
George Wilson: I was husky.
Dennis: How old is this bed?
Mrs. Martha Wilson: It belonged to my mother.
Dennis: Where's she sleeping now?
Mrs. Martha Wilson: She's been gone many years, Dennis.
Dennis: On business?
Mrs. Martha Wilson: No, she's in Heaven.
Dennis: Oh, there's an awful lot of people in Heaven, especially old people.
Answer: Because of what George said to him in the house after he was robbed. He hurt Dennis' feelings so he ran away.