A second method, which produced longer messages, was the substitution of slates. If this message was of a general character the slate was _switched_ for one bearing a previously written message concealed about a nearby piece of furniture. If a special message was required it was written by an assistant listening in the next room. When the slate had been cleaned ready for the message the Doctor gave the cue and the assistant rapped on the door. The Doctor answered the knock in person, taking the slate with him, and while listening to some commonplace report the slates were exchanged. On resuming his seat the slate was placed under the table leaf as before. No sound of writing being heard, he would examine the top of the slate several times but of course find no writing. Finally, claiming that the influence did not seem powerful enough, he would lay the slate on the top of the table, message side down with a piece of pencil under it, and then take both the hands of the sitter in his. Soon a sound of writing would be heard and on examination the message would be found. It was possible for Slade to produce the sound of writing while his hands were holding those of his client by slipping a piece of pencil through threads on the side of his knee and rubbing it against another piece held to the table leg by a wooden clip. One of the most common methods of slate writing is known as the “flap slate.” The message is written beforehand and concealed with a flap of silicated gauze, or thin slate, which fits closely within the slate frame. One side of this flap is covered with cloth to match that used on the top of the table and when it is dropped is unnoticed. A better way is to cover the back of the flap with newspaper and by dropping it on a newspaper it becomes invisible.