“"You look like a girl with a secret," Matt said. "I think it must be the smile."
She moved closer to him, which was very close, and lowered her voice. "Can you keep a secret?"
Matt smiled with one side of his mouth to show that he knew what was coming. She said it anyway. "So can I."”
Source: A Gift From Earth (1968), Ch. 2 : The Sons Of Earth
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She moved closer to him, which was ve…" by Larry Niven?