Weasels, by their nature, tend to have their own good reasons for whatever they are up to and however they are doing it. Cunning and sly, if a weasel ever sets a puzzle before you, you should be careful not to be too distracted by it. Small edible mammals are particularly vulnerable — tricked into unwariness by a distracting crossword clue or baffling number trick, they’re snatched and gobbled up. It is a ghastly way to behave.

So if there were to be a weasel right at the start of Planetarium, you could be sure there’d be a reason for it. But as it happens, this weasel’s motive is fulfilled — its obligation has already been discharged, and it has nothing more to do. And although it could easily present a riddle or puzzle that might mesmerise you like a paradox might numb a vole, it doesn’t. In fact, this is because it has already done so, although perhaps you don’t yet know it.