[3][4] Based on the general principle of interaction between waxy and translucent layers, similar devices varied in design and were produced by different companies over the world.

[5] Sigmund Freud described such Wunderblock, comparing it to "the structure of the perceptive apparatus of the mind" in his 1924 "Note on the Mystic Writing-Pad" (later mentioned by Jacques Derrida in Writing and Difference).

[12] They licensed production of the toy with its frame decorated with pictures of comic book heroes, such as Batman and The Hulk, Disney characters, such as Mickey Mouse and Bambi, and popular stars from TV shows and films.

[1] Jeremy Duns stated in his 2013 book Dead Drop: The True Story of Oleg Penkovsky and the Cold War's Most Dangerous Operation: In 1952, an electronic sweep of the American ambassador's residence had revealed that a wooden replica of the Great Seal of the United States that had been a gift from a Soviet youth group at the end of the war contained a listening device.

As a result, the Americans were convinced that microphones were hidden throughout the embassy, and some staff had taken to communicating with each other by writing on children's Magic Slate doodle pads, which they would wipe clean after each message so that no trace of sensitive conversations remained.

[10] In a covering letter to then President Reagan, Secretary of State George Shultz and the Director of Central Intelligence, the publisher wrote: "We are not often called upon to serve our country's defense, so we are pleased at the prospect of making a contribution.

It takes place in a monastery where the monks and nuns observe a vow of silence and communicate with each other using Magic Slates decorated with colorful cartoon characters.