More like two tetrahedrons stuck together.
Octahedron https://en.wikipedia.org/wiki/Octahedron
Eight sided three-dimensional shape. Often this looks like two pyramids stuck together at their bases.
A hexahedron or a triangular dipyramid. This is the shape formed by two triangular pyramids (tetrahedrons) stuck together along one triangular face.
Put ice in the inside one and rub the out one. The ice will result in thermal contraction and the friction in thermal expansion. Neither will be large but should be sufficient.
heat them (with a lighter, or the oven or sumthin), then slide slowly away from each other.
A molecule
Two amplifiers stuck together.
lute
two cat fish stuck together
10cm2
A chain reaction is more likely to occur in two separate pieces of uranium-235 due to increased chance of neutron interactions. When two pieces are stuck together, neutrons are more likely to escape without causing additional fission reactions.
two pairs of glasses
More like two tetrahedrons stuck together.
It is called interlocking, where two objects become entwined or stuck together after a collision.
They do no such thing
Two tetrahedron stuck together by a face.