At first your students might think there really are ghosts in your classroom, but after your demonstration, they will understand that the science of optics and index of refraction is behind your spooky tricks. Dare students to stick their hands into a jar of invisible ghost eggs, then make the eggs appear by adding some glowing dye to the water. Then investigate vanishing ghost poop in another cool science experiment. Requires strict adult supervision. Keep out of reach of small children and pets.