The first 100 people to use code SCIENCE at the link below will get 60% off of Incogni: https://incogni.com/science Steffen's polyhedron is a flexible concave polyhedron. Euler thought such a shape was impossible. I also show infinitesimally flexible polyhedrons and bistable polyhedrons. Here's Ivan's channel: null Here's my Discord server: https://discord.gg/B6uNzAgshy Additional filming by Nicole Jacobus You can buy my books here: https://stevemould.com/books You can support me on Patreon and get access to the exclusive Discord: https://www.patreon.com/stevemould just like these amazing people: Tj Steyn Pavel Dubov Lizzy and Jack Jeremy Cole Brendan Williams Alan Wilderland Frank Hereford Lukas Biewald Damien Szerszinski Heather Liu Grant Hay John Zelinka Paul Warelis Matthew Cocke Nathan Blubaugh Twitter: http://twitter.com/moulds Instagram: https://www.instagram.com/stevemouldscience/ Facebook: https://www.facebook.com/stevemouldscience/ Buy nerdy maths things: http://mathsgear.co.uk/