When hearing, but not seeing, this, is the only clue to it being 'dem' rather than 'de' the adjective that follows? i.e. Couldn't 'vad gör de ...' mean 'what do they do/make ...'? I misunderstood this sentence as 'What do they do efficiently?' but now I see it couldn't be that, because it finishes with an adjective rather than an adverb.