Triangular prism and it's transformation
We get this model from the box; it is in a set separately from all other models. We close all sides. Then we pull A1BA1C, and we obtain a regular triangular prism.
Opening the AB, AC and BC we obtain the truncated pyramid. Further, extending BB1 until the B1A1, A, B1, C1, C become straight lines, we obtain a triangular pyramid ABCB1, where different sections of a triangular pyramid are visible. This model is of interest that the simple turning from side to side generates more and more new pyramids with various sections.
We hold from top B1 and pull in order to obtain a pentagonal pyramid. All other sides are B1A, B1B, B1C1, B1C1 and B1A1.
We increase the sides of the quadrangle ABCA1, turning it into quadrate. We compress the C1B1 till the end and move upwards and inwards the top C1 and bring it up to the osculation with CA. As a result we obtain a tetragonal pyramid with the height B1C1. For receiving a pentagonal pyramid again we close all sides.
The triangular prism turns into the regular hexagon, and you can obtain it yourself
To obtain an octahedron from this model (regular octahedron), we do the following. Strongly holding from the top C and twisting CA1 midstream completely separating from the top C. In the same way we separate CA1 from A1. Then CA1 is strengthened in tops A and C1. Closing all sides, we obtain an octahedron.