In "All My Sons", Mrs. Keller (Kate) says to Keller: "Be smart now, Joe. The boy is coming, be smart." What does she mean?
When Kate Keller says these words to her husband, she is referring to the fact that George Deever, Ann's brother, is on his way to the Keller home. She is very concerned about George's need to speak to his sister. She is also very concerned that George has been to the prison to visit their father. It is obvious that he is coming to see Ann to give her some information that he learned from his father.
Kate is worried that George is coming to the Keller home to talk about opening the case that put Steve Deever in jail.
"Kate and Joe, on the other hand, are still locked in tension and conflict. The curtain falls on an atmosphere of suspicion and suspense as Kate questions Joe and admonishes him to “be smart,” presumably about the chance that he can withstand the cross-examination to come and the possibility that he finally must change his story about his involvement in the crime blamed on Steve."
Kate is much more tense than Joe Keller from the very beginning of the play, and when she learns that George Deever is coming to her home, she feels that her husband's relaxed, casual behavior will get him into trouble. This is particularly illustrated when Kate scolds Joe for playing jail and policeman with the little boy Bert. It irritates Kate that Joe can joke about a topic that is so sensitive, considering that Joe went to jail for a time.
Kate's nerves are jumping with worry that Joe will say something incriminating when George starts to question him about the events that led to his father's imprisonment.