spilt (4D) milk

The most famous 40 shape is the Klein bottle, but it's actually a terrible choice for a bottle. In Ford I mentioned the Klein bottle forms an endless loop, but when we depict it as a 3D model, a self-intersection is unavoidable. These self-intersecting 3D models can hold liquid, but a real Klein bottle in its 40 habitat has only one side. Milk poured onto a 40 Klein bottle might just splash onto the floor, since it doesn't actually enclose a volume.