In August 1946 Escher created a mezzotint of a mummified frog. He rarely used this technique, despite the subtle nuances in tone it can achieve. The choice of both subject and composition are atypical for this period, in which he experiments with tessellations and geometrical shapes. He depicts the skeleton exactly as he sees it. Escher found the frog behind a piece of furniture in his own house. He printed the work himself on his own press, in an edition of 24 copies*.
Although the mezzotint is more suitable for detailed and realistic work, Escher would create two prints in which he used tessellations and geometric shapes: Crystal (December 1947) and Plane Filling I (March 1951). But Plane Filling I would be the last one. The technique proved too time-consuming at a time when the demand for his work was increasing robustly. In any case, these experiments mean we can continue to admire this dead frog with its odd gaze.
Source
[*] Wim Hazeu, M.C. Escher, Een biografie, Meulenhoff, 1998, page 305