Answer:
Selecting a jury is challenging for the person will always try to think of his own safety first before making up his mind. Also, people hate to be put on a spot where they have to chose either one, which will make them an enemy of the other.
One of the Cunninghams on the jury wanted to find Tom not guilty.
This surprised Jem for he thought that they hated Tom and wanted to hurt him. Moreover, he had acted against the interest of his own white people which surprised Tom.
Explanation:
Harper Lee's "To Kill A Mockingbird" revolves around the theme of racism and the lives of the people in the South. Through the Finches' family, Lee uses the youngest Scout to highlight the issues and situation of the Southern town of Maycomb, Alabama.
Atticus Finch is a lawyer, who represent the ra pe accused Tom Robinson from being convicted and put to death. Tom had been accused by Bob Ewell who, like most whites, had a dislike for all colored people. Atticus tells Jem that selecting a jury is hard, especially for cases like this as it involved a colored man. For, even if the jury thinks and knows that the accused is not guilty, he will act contrarily to ensure his safety and not anger his fellow people. He would rather chose his own skin over the life of the innocent man. Atticus also mentioned that people don't like to be put on the spot and made to make up their minds.
One of the Cunnighams was put on the jury for Atticus believes that they are fair-minded. It was this Cunningham that wanted to acquit Tom from the accusation
This act of not finding Tom guilty by one of the jurors surprised Jem for he believed that they(the whites as well as the Cunninghams) were against a black man and had wanted to hurt him.