As my sister was leaving me, she paused at the door and looked back.

"Tell me, " she said. "Have you ever heard anyone whistle in the dead 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 it has awakened me. I cannot tell where it has come from - perhaps from the next room, perhaps from the lawn. I thought I would just ask if you had heard it. You don't whistle when you sleep, do you?"

"Certainly not. I have never heard this whistle. But I sleep more heavily than you."

"Yes. Well it is of no consequence anyway."

My sister went away and a few minutes later I heard her key turn in the lock. We always used to lock ourselves in our rooms at night. The cheetah and the baboon roaming the gardens caused us no feeling of security.

I myself went to my bed soon after.