In paragraph 47 (“the first light...”),

In context, this shows that Siddhartha is a bit nervous.... the trembling betrays his feelings. His face, however, is completely calm and tells his father that he is resolute in his decision.

The first light of day shone into the room. The Brahman saw that Siddhartha was trembling softly in his knees. In Siddhartha's face he saw no trembling, his eyes were fixed on a distant spot. Then his father realized that even now Siddhartha no longer dwelt with him in his home, that he had already left him.