A flexible polyhedron due to C. Schwabe (with the appearance of having four horns) which flexes from one totally flat configuration to another, passing through intermediate configurations of positive volume.
Quadricorn
See also
Flexible PolyhedronExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Quadricorn." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Quadricorn.html