Nabokov’s 'dark dog nipples'

As I’ve been commenting on the role of editors and, to a lesser extent, translators, I was reminded of an anecdote I read many years ago, concerning the translation of one of Vladimir Nabokov’s novels by his son Dmitri. Describing a railway train, the original text, as I recall, referred to ‘a row of dark dog nipples’ on the roofs of the carriages. Dmitri, rather naively, initially offered the translation ‘ventilators’. This was knocked back by the famous father: ‘there are no ventilators on my train’.