Elephants and Bats, Khao Yai N.P.
DId they ever. About 15 minutes after sunset, as th last of the light was dying from the sky, there was a roar, and a blurred streak in the darkening sky. The noise was from what must have been millions of bats leaving their caverns for the night. THe stream of bats waved across the sky like slow motion electricity, and the noise built to a peak and then quickly died down.
An awesome way to finish a holiday.