Mr. Grumpy’s Secret

Oh, the heat is unbearable! Julia and Sam can’t stand this weather but nobody is as grumpy about it as Mr. Grumpy. When he meets the two friends in the hall, he asks Sam to water his plants when he’s away. Both mice agree to help their neighbour but he won’t even thank them. Julia is so outraged by this that she gives up in the beginning but she comes to help Sam eventually. They notice a painting that hangs with its face turned to the wall. What does it show?