As silly as a rook

"As silly as a rook." my wife said. I said, "What does that mean?" She said, "Its something people say." I said, "I never heard of that before!"

Are rooks silly? At dusk they congregate at the top of horse chestnuts near our house, numbering eighty, maybe a hundred, then, with an agreed squawking, they launch into the fading light all at once, across the fields and back again, breaking like the Red Arrows then regrouping. If you watch carefully you will see they fly in pairs, swirling around each other in a strange choreography, ballroom dancers of the air.