The PE teacher was doing his stuff - in the classroom, of course, not in the gym - and struggling to elicit correct responses to his lesson on vital parts of the body, essential for physical development.
His charges sat stumm and blank asthe resourceful teacher pointed deliberately to the front of his leg, the bit between your knee and your torso. "And what do you call that muscle?" he asked again.
At last a lad offered an answer. "Is it the "thigh-roid, sir?"