Trilling your "Rs" is so easy.....it comes naturally.....but for nearly all English people (at least) it appears to be impossible. All you do is vibrate the epiglottis...easy peasy.....like a "dry" gargle.
Which trill "r" are you talking about, though? There are two: [r]* and [R].
Damian is talking about, the uvular trill, [R]. There's also an alveolar trill, [r].
Note: I'm using the IPA not Tom's ASCII alphabet.
http://www2.arts.gla.ac.uk/IPA/fullchart.html
The uvular trill (vibrating the epiglottis) is present in German, French and other northerly languages of Europe. For languages in which it is not present, it is difficult for its speakers to produce. For example Icelanders (though northerly) and Italians use the alveolar trill (tongue trill) for "R" so for them the uvular trill is troublesome. The English "R" is totally unrelated to either trill that's why they appear to be "impossible" to the English.
There're not impossible though: it just takes pratice.
"They're not impossible ..."
Also the asterix after the "[r]" was to connect to the footnote: I forgot to put one in front of the footnote.
"... it just takes practice." Eye reellie karn't sbel.
It takes a LOT of practice which is too much for most people who end up reverting back to their old "proper" pronunciations.
Perhaps I'm special but it never took me any practice: I could just pronounce them both. I don't know why. I can also touch the back of my throat with my tongue ... did you not want to know that?
It's a lot harder to pronounce them consistently in meaningful language if you're not used to doing so. If you were raised in an environment where many languages were spoken around you, it's not so surprising you can pronounce both with little effort.
I wasn't raised in such an environment but I have to concede that I cannot "pronounce them consistently in meaningful language": this is because I don't speak any language which uses them.
When I say "cannot" perhaps I should say "do not": perhaps I could if only I knew such a language.
The uvular trill of German & French seems easy to me. The trilled rrrrrr of Spanish, etc., however, is more of a physical impossibility.
Even though that kind of R is used in my native language, I used to have a lot of problems with it, I guess it's a slight disability.... LOL :) I learnt to speak too early (I wasn't even 1 year old), so I got some bad habits which of course I don't have anymore, but that "R" problem stayed (I just can't vibrate my tongue and say RRRRRR, even though I can pronounce it normally in all the words).
I, on the other hand, have trouble with the uvular trill, but the alveolar trill such as in Spanish and Italian is quite easy for me. Perhaps it has something to do with the languages we learned in our youth? I learned Spanish at a very young age, so the alveolar trill has never been difficult.
Well, I'm happy to say that I can (now) pronounce them all, plus the Danish uvular continuant.