When explaining the Chord Theorem: The perpendicular bisectors of chords always intersect at the center of the circle. I draw a cresecent on the board and explain that when paleontologist find fossils, a lot of times they are missing certain fragments, and sometimes they just find a piece of the skull (crescent drawing). So one way they are able to recreate the actual size of the dinosaur is to draw chords along this fossil (Draw three chords along the inside of the crescent), and then by perpendicularly bisecting the chords (draw perpendicular bisectors) they find out where the center of the skull is and recreate the rest using that center. They can then recreate the rest of the body size by using proportions of what they know from other dinorsaurs. All this from one skull fragment. (Also works with a human skull fragment, but dinosaurs are less morbid).