Saul Goldie -- Likewise, a substantial number of English-speakers evidently cannot say the nasal U as it occurs in the French pronoun “tu”, or the German preposition “über”. I have never understood this phenomenon, but I've been told that these people either do not hear the difference in sound at all, or never learn the placement of tongue and lips required to produce it.

As for the rest ... Well, the things we cannot say in public, we are rarely unwilling to say only too often within the charmed circle of our friends and relations -- who probably wish we would stop.