Antonia Forest fans

I just found the passage, and Peter reflects that she's 'an excellent example of what Lieutenant Foley had once referred to disparagingly as that useful social and examination-room accomplishment of making a pint of knowledge fill a hogshead of ignorance'. (He then of course hates that he's thought about Foley.)

It is a useful skill - and especially if you know you're doing it and therefore are on the look out for additional knowledge.