What did Rab do that angered Johnny? Why would he be angry about his?

One day, Johnny returns to the Observer’s office to find Cilla there. She is laughing with Rab and drawing a political cartoon for the newspaper. She impresses Johnny with her beauty and her artistic talent, and he is jealous that she seems to be paying more attention to Rab than to him. Rab also eats an apple that symbolizes Johnny's love for Cilla.