The Secret of Parabolic Ghosts

From Mathologer.

Today we’ll perform some real mathematical magic—we’ll conjure up some real-life ghosts. The main ingredient to this sorcery are some properties of x squared that they don’t teach you in school. Featuring the mysterious whispering dishes, the Mirage hologram maker and some origami x squared.paper magic.

Here is a nice article about the Mirage hologram gadget. A complete ray-trace analysis of the Mirage toy by
Sriya Adhya, John W. Noé. The history part in particular makes for a fascinating read:

As usual, thank you very much to Marty and Danil for their help with this video.