A girl called Nadia has a younger brother whose brain works a bit differently. He lines his toys up just so, gets upset by loud noises, says the same favourite facts over and over. Usually Nadia is patient. But one day, with friends around, she did an impression of him — the hand-flapping, the repeating — and her friends laughed. It felt good to be funny. Then she noticed her brother had come into the room. She doesn't know how much he saw or understood. He didn't say anything. He just went very still, then quietly left, and Nadia's stomach dropped.