This ambiguous (or reversible, or bistable) figure commonly referred to as the duck-rabbit was originally noted by the American psychologist Joseph Jastrow (1864-1955) in 1899. Before he noticed the difference, the image was regarded as a simple illusion for the amusement of children. Along with similar figures such as the Necker Cube and the Schroeder Staircase, Jastrow used the duck-rabbit to point out that perception is not just a product of the stimulus, but also of mental activity—that we see with the mind as well as the eye. Jastrow published his own version of the cartoon based on one originally published in Harper’s Weekly (November 19, 1892, p. 1114).  The Harper's cartoon, in turn, was based on one that had appeared earlier that year in Fliegende Blätter, a German humor magazine published in Munich (October 23, 1892, p. 147).