While the Penroses credited Escher in their article, Escher noted in a letter to his son in January 1960 that he was: working on the design of a new picture, which featured a flight of stairs which only ever ascended or descended, depending on how you saw it. form a closed, circular construction, rather like a snake biting its own tail.
Trong khi nhà Penrose ghi nhận Escher trong bài viết của họ, chính Escher đã tự ghi nhận trong một bức thư gửi cho con ông vào tháng 1 năm 1960, đề rằng: working on the design of a new picture, which featured a flight of stairs which only ever ascended or descended, depending on how you saw it. form a closed, circular construction, rather like a snake biting its own tail.