That Sunday dawned unspectacularly normal.
The sun rose, the clouds passed and all seemed right with the world.
The arrival of the alien device went almost without notice.
Then the animals began to howl.
Their sensitive hearing was abused by a sound which caused them to shout their outrage.
It went almost unheard by humans because it was outside their narrow frequency range.
Those few who sensed without reason the low decibel tone ran.
They could not go far enough.
Not for some years was the result obvious. It was discovered to be a selective mammalian birth control which affected only one species: H. sapiens.
Dwindling numbers found themselves childless. They took shelter in conformity.
It was all over in less than a hundred years.