What noise are George and Lydia concerned about coming from the nursery?

George and Lydia are anxious in general over the amount of time their children, Wendy and Peter, are spending in the nursery, watching scenes of the African veldt on their giant viewscreens. However, what most worries them are the repeated screams they hear as the lions kill their prey. The lions appear bloodthirsty and frightening, and the screams, for some reason, sound familiar to the parents.

The whole panorama of the veldt troubles the parents deeply: it is a hot, unpleasant and savage place, with animals feeding on bloody meat and vultures circling overhead. Wendy and Peter seem obsessed with it. The parents decide, finally, that they are going to shut down the nursery and start afresh, which upsets the children greatly. Only at the very end of the story, when they are trapped inside the nursery, do the parents realize that the screams they have been hearing are their own.