She gave him a shy smile, "I used to work closely with your father on a few of his pet projects. I became extremely familiar with his preferred layout of lab equipment. If even one beaker was not facing "the right way" then he would snap a meterstick over my knuckles repeatedly." He looked at her astonished, but she could see his mouth was starting to form further inquiries. So, she added, "He was right-handed. It was clear the last person to touch any of the equipment in that lab had to be someone else, someone less meticulous and... left-handed."