What I saw was the quick movement of a section of the wall behind me. It was turning upon pivots, and with it a section of the floor directly in front of it was turning. It was as though you placed a visiting-card upon end on a silver dollar that you had laid flat upon a table, so that the edge of the card perfectly bisected the surface of the coin.
The card might represent the section of the wall that turned and the silver dollar the section of the floor. Both were so nicely fitted into the adjacent portions of the floor and wall that no crack had been noticeable in the dim light of the chamber.
As the turn was half completed a great beast was revealed sitting upon its haunches upon that part of the revolving floor that had been on the opposite side before the wall commenced to move; when the section stopped, the beast was facing toward me on our side of the partition--it was very simple.