Once upon a time I was hanging out with a fairly international group of people. Somebody sneezed, and one of the Americans reflexively responded, "Gesundheit!"
A German in the group seized on the opportunity to ask, "How do all Americans know this word?" Apparently he had been puzzled for quite some time by the number of Americans who know one, and only one, word of his native tongue. Some of them don't even know that it is a German word!
None of us could come up with a satisfactory answer.