What anamorphic symbol appears in Holbein's French Ambassadors?

In Hans Holbein the Younger's painting "The Ambassadors," the anamorphic symbol is a distorted skull located at the bottom of the canvas. This skull serves as a memento mori, a reminder of mortality, contrasting with the opulence and intellectual pursuits represented by the two ambassadors. The unusual perspective of the skull can only be properly seen from a specific angle, emphasizing the theme of perception and the fleeting nature of life.