The motion tracker said they were within five metres, but the room was more than five metres across and visibly contained no hard-to-miss enormous slavering death-machines. Then someone got a nasty thought, boosted themself up to the ceiling, and lifted one of the ceiling tiles. The ceiling space was crawling with the things.

But they always hide in the ceiling! You'd think they would have thought of that by now.

In the old Cavendish, the weather does hide in the ceiling - you get a day of heavy rain and then a day or so later water starts dripping in through the ceiling and the bacterial colony in the carpet smells of fish again.