>>>PS FYEngI "behaviour" (English spelling) is only ever singular
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>>So was milk in my language, until they introduced the various levels of skimming, and the CEO of the dairy factory had to say a sentence with "what happens with all those diferent... ... ...milks".
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>Well, he could have said "...all those different... types of milk".

He really got confused at that point, stumbling into plural cases of milk. You could hear the confusion in his voice :). As the actor said, "confuse the curtain, I got pulled down".

>>I think I've seen "behaviors" in articles on OOP, specially on design patterns, that's where I got it from.

>>Are trousers singular or plural? It depends - from above, they're singular; from below, they are plural.
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>Don't understand the above and below ref. I'd say always plural as "pair of ..." is understood. However, in a men's outfitters, as one is trying on some kecks (N. English), you might hear the shop assistant (clerk) say, "Yes, they are a nice trouser, they are", which is even more confusing as a plural pronoun is being equated to a plural-only noun, referred to in the singular. (similarly "they are a nice jean...", but you never hear an optician say "They are a nice glass". Go figure!

Well, I think you got my drift, even though the trouser(s) example has lost a lot in translation. We say "one trousers", "one underpants", "one glasses" - but the word "one" is in plural :).