Describe the circumstances that lead David to make this discovery of Petra’s special powers. How do Petra’s special powers of telepathy almost lead to the discovery of the group?

In Chapter Nine, David recounts his discovery that Petra also has a gift of communicating without words. He is working in the field one day when he suddenly is hit with a pain in his head. He drops what he is doing and goes running off in the direction he is being telepathically called in. He does not know where or why he is going, but he is compelled to go. As he runs toward the stream, he sees Rosalind running down the other side of the bank. David dives into one of the pools of the stream and retrieves Petra, who is precariously clinging onto a bush to avoid being swept away by the current. David and Rosalind discuss what happened, and conclude that Petra is far more powerful than either of them because she is able to issue commands to others. At that moment, other people approach the three of them, because they had been alarmed by how quickly David and Rosalind had run to the spot. David and Rosalind lie to avoid suspicion: they say they both heard Petra screaming.