A pug mill is a machine consisting of a large cylinder with a central shaft passing through it from top to bottom.
This is called "pugging," and the whole thing—trough, shaft, and knives—is a "pug mill."
In what is called the "soft-mud" process, the clay is pushed on by the pug mill to the end of the trough.
The first machine used to do all this work goes by the humble name of pug mill.
