It hung round the neck of someone, and that someone was watching them through a chink, high up in the wall, specially devised for watching people who were imprisoned.

But they did not know.
There was nearly an hour of anxious waiting.

They tried to take an interest in the picture on the wall, a picture of harpers playing very odd harps and women dancing at a feast.

They examined the painted plaster floor, and the chairs were of white painted wood with coloured stripes at intervals.
But the time went slowly, and everyone had time to think of how Pharaoh had said, 'Don't torture them--YET.' 'If the worst comes to the worst,' said Cyril, 'we must just bunk, and leave the Psammead.

I believe it can take care of itself well enough.
They won't kill it or hurt it when they find it can speak and give wishes.