The puzzle above is relatively simple to construct; this is a pressed or forced assembly evident by the chamfered hole and inserted section. Often one end of the insert is soaked in water to aid in assembly.
The two puzzles below, while based upon the same concept as above, are not simple pressed assemblies. The shoulders are exceptionally large adding to the mystery of assembly. My "guess" is the insert was either boiled, or soaked in a mixture of water and alcohol; then compressed, inserted, reconstituted and dried.
(but that is only a guess)
This is something I carve when I have to wait somewhere; all it requires is a 2x2x6" Block and a sharp pocket knife.
The fine details I finish later.