Selling a used copy of Outs, Precautions, and Challenges for Ambitious Card Workers by Charles H. Hopkins. This is a staple-bound paperback booklet. Light yellowing from age, regular wear from use. There's a penciled in price on the cover page. All pages intact and fully readable.
The magician takes a pen and sticks it through the Invisible Zone case. When the case is opened the center of the pen is totally invisible even though the pen is moved back and forth! This one looks totally impossible.