'look , that 's my hat , if you do n't mind do n't you dare do that to my- ' he leapt across the floor and was rewarded with a thump across the side of the head , which would have astonished him if he 'd had time to think about it ; the librarian might shuffle around the place like a good-natured wobbly balloon , but underneath that oversized skin was a framework of superbly-cantilevered bone and muscle that could drive a fistful of calloused knuckles through a thick oak plank .