In all the figures below, all the black lines can be seen by you,
the reader.  The green lines cannot be seen by you, the reader
Neither can the dotted red lines be seen by you, the reader.




If we place the knife or saw along the edge closest to you, and
cut down toward the back bottom vertex, along the two red dotted lines,
shown here,



then we will have these two pieces:

.

The piece on the left has 4 faces, and the piece on the
right has 5 faces, making a total of 9 faces.

Edwin