Crayfish update. We "set him free" one day. He liked to move backwards away from us. Wasn't heading for the stairs fast enough so we picked him up and moved him over there. He was very able to get down the stairs - which are past vertical as DH pointed out. He used all his little legs/claws to hold on securely to the carpet and headed easily down - face first. One day grainy dark video may come to a YouTube near you...