On Fri, 19 Jan 2007 21:52:07 -0600, Eric Christopherson <[log in to unmask]>

>On Jan 19, 2007, at 5:06 AM, John Vertical wrote:
>> Eric Christopherson wrote:
>>> What's being trilled, then, when you pronounce a uvular trill?
>>> (I've  never been clear on why some languages have a uvular trill
>>> or  fricative or approximant but not a velar one.)
>> The uvula. Can't generalize that to just any POA, can you?
>Ah -- so with say a coronal trill, the tongue is moving against the
>roof of the mouth, but in a uvular trill the uvula is moving and the
>tongue stays stationary?

The few detailed descriptions I've read describe the back of the tongue
forming a groove in which the uvula vibrates.

Trills occur when the thing that is trilled is held just loosely enough that
air-pressure (the Bernouilli effect) can cause it to vibrate. Four things
(not counting the glottis or aryepilgottal folds) can trill: the lips,
tongue tip, tongue edge (a 'lateral trill', described by Catford, but
otherwie not often mentioned in the phonetic literature), and the uvula.

For labial trills I think there are three or four possibilities: 
*  bilabial (both lips vibrate); 
*  labiodental (lateral channel cause upper lip to vibrate against teeth)
*  linguolabial (lower kip vibrates against underside of tongue)
*  labiolingual (upper lip vibrates against tongue tip/blade - though this
might also actually be an interlabial trill, where the tongue tip protrudes
between the lips and vibrates)
The last two are variations of the Bronx cheer or raspberry.