Steve Barnes' World of Happiness

The coveted bivalvial trill.

Incidentally, I took note of the word "bivalve" when sharing the definition of "cockle" earlier – it just refers to a mollusc with a hinged shell.

It reminded me of the word "bilabial" (any sound involving the lips), which reminded me mainly of the linguistic term "bilabial trill": that vibrational, motorboat-like pronunciation. (Other common trills include the lingual trill, or rolling your "r," and the guttural trill, heard when gargling with or without liquid.)

Anyway, this inspired me to consider the possibility of a "bivalvial trill": the hypothetical vibration of a hinged shell. I'm not sure whether this has ever existed in nature, but now that I've wondered about it, I'd be especially enthused to know it does.