What does Beah mean when he says, “My teeth became sour as I listened to his story” a long way gone chapter 11

Beah meant that he couldn't bear the brutality of the incident that happened to his friend, Saidu. He felt terrible and sensitive  to what happened to Saidu's family as Saidu narrated it to him.

Explanation:

The question is related to the story entitled, "A Long Way Gone: Memoirs of a Child Soldier," which was written by Ishmael Beah. The story centers on Beah's struggles as a "boy soldier" during a civil war in Sierra Leone.

The question above happened when Saidu talked to Beah about what happened to his family when the rebels attacked. They were among the people who couldn't flee the town. Saidu was in the attic hiding when the rebels attacked his father, mother and three sisters. After hearing Saidu's story, Beah then understood why Saidu was always quiet.