The Damned Thing

"There are sounds that we can not hear. At either end of the scale are notes that stir no chord of that imperfect instrument, the human ear. They are too high or too grave. I have observed a flock of blackbirds occupying an entire treetop--the tops of several trees--and all in full song. Suddenly--in a moment--at absolutely the same instant--all spring into the air and fly away. How? They could not all see one another--whole treetops intervened. At no point could a leader have been visible to all. There must have been a signal of warning or command, high and shrill above the din, but by me unheard. I have observed