When my sister was leaving me, she stopped at the door and looked back.

"Tell me," she said. "Have you ever heard anyone whistle in the middle of the night?"

"Never," I said. "Why do you ask?"

She replied, "Well, for the last three nights, always at about three in the morning, I have heard a low clear whistle. I am a light sleeper, and I cannot tell where it has come from. Perhaps it is from the next room, perhaps from the garden. I thought I would ask you if you had heard it. You don’t whistle when you sleep, do you?"

"No. I have never heard this a whistle. But I sleep more deeply than you."

"Yes. Well it is not important anyway."

My sister went away and a few minutes later I heard her lock the door. We always used to lock ourselves in our rooms at night. The cheetah and the baboon walking around in the gardens caused us to feel unsafe. A few minutes later I went to bed as well.