In another thread I mentioned the Berlin translation of 'Mind the Gap' (Bitte beachten Sie den Abstand zwischen dem Wagen und der Bahnsteigkante) as an instance of practical untranslatability. But clearly it isn't, as one can do it in three syllables in German, as someone pointed out (Achtung Spalt!) and also say, in English, 'Please mind the gap between the door and the edge of the platform.'
The interesting question is: why is the short version more acceptable in English than in German?
Some light on this is cast by the widow of the actor who made the classic recorded announcement. She specifically mentions that the announcement was 'not a whole paragraph about the edge of the platform'. You can hear her thoughts at http://www.youtube.com/watch?v=mj24JtTOEm8
This clip also contains a clear playback of the announcement.
As a phonetician, I was interested in comparing this with other 'mind the gap' announcements, which seem to be made by station staff rather than professional actors (you can hear a variety on youtube). Some of the latter appear to be imitating the classic version, while others introduce the word 'please'.
The iconic version has a two-tone-group structure (which is fairly unusual for three syllables). 'Mind' has a rise-fall-rise, and so (though more subtly) does 'the gap'. This may be why the exhortation is not perceived as a brusque instruction in spite of its brevity. Some of the imitators have a simple high fall on 'gap', but the rise-fall-rise on 'mind' is always there, and it's still a two-tone-group structure.
The modern versions including the word 'please', on the other hand, have a single falling intonation, with the nucleus on 'gap'. This would sound harsh, but for the 'please'. As for the ten-word version at Heathrow (I think), I imagine no one even notices it. L'art d'ennuyer, c'est tout dire.