When Gasemu and Beah first meet in the forest in Chapter 11, Gasemu tells Beah he looks different to him because…

Gasemu says he looks different because he has lost the glow on his forehead..... Beah looked sad.

“I see that you look very sad. Your forehead used to glow naturally when you were just a child. Your parents and I used to discuss how unusual that was. We thought it was because you were happy all the time.