voluntarily sever, then regrow, their spinal cords voluntarily sever, then regrow, their spinal cords voluntarily sever, then regrow, their spinal cords voluntarily sever, then regrow, their spinal cords voluntarily sever, then regrow, their spinal cords voluntarily sever, then regrow, their spinal cords voluntarily sever, then regrow, their spinal cords voluntarily sever, then regrow, their spinal cords voluntarily sever, then regrow, their spinal cords voluntarily sever, then regrow, their spinal cords