[2] This is possibly the most simplistic prop design as these props were either found objects in the case of the pebbles, or in the case of the urns terracotta or possibly bronze was used to craft them.
Back then prop design was not advanced enough to build, or create a skull.
This resulted in grave diggers being hired to go and find the needed skulls.
[3] If the prop did not require the digging of graves it is most likely hand crafted from wood, metal, stone, or sewn from cloth.
Shakespeare's played used natural props such as trees, and moss banks that were brought on stage for A Midsummers Night Dream.