This was at the Science Museum in Valencia, Spain. Although it looks impossible, this solid metal bar can pass through a curved slot. It works because the rod is angled and rotated through space by a three-dimensional shape with a hyperbolic cross-section. Therefore if the slot is the exact shape of this hyperbola, the rigid straight rod can pass through it.
It’s a really good thing to look at if you want to know how time/space is curved. What the hole in the plastic represents is not the shape of the pole but a cross-section of the pole plotted against time. Really nice geometry.
