牢实

牢 = 宀 + 牛 : Sir Lancelot (l) keeps a bull (牛)in the aorta's kitchen (ao2) by imprisoning (牢) it in a very sturdy (牢) graduation cap (宀).

实 = 头 + 宀 : Sherlock Holmes welcomes professor Skull just inside the entrance of the space station. Professor Skull has not a complete head but only a skull, and a solid understanding of solid state physics. She really is an honest person and still wears her graduation cap.