The blivet is an undecidable figure, an optical illusion and an impossible object.
It was known in 1964, and one was shown on the March 1965 cover of Mad Magazine.
An anonymously-contributed version described as a "hole location gauge" was printed in the June 1964 issue of Analog Science Fact/Science Fiction, with the comment that "this outrageous piece of draughtsmanship evidently escaped from the Finagle & Diddle Engineering Works".
It is also called a "two-pronged trident" and a "three-legged widget".
