I've had them since 1968. They are trick decks, often called Svendali Cards or mechanical decks. Their aire of secrecy may be an extension of the Magician's Code, i.e., not to explain or reveal how tricks are done. Always a staple at any magic store, in the 60's and 70's they were 'pitched' at State Fairs, Expos, County Fairs and the like. In the 80's there were TV commercials for a trick deck called TV-Magic cards, those decks were the same as the Fox Lake Svendali decks, and may have come from Fox Lake (with a different back).

Although possible, I have never seen Fox Lake decks as regular decks, i.e., 52 cards, 13 cards each in 4 suits.

I gotta say, the two foxes are identical!

Jim