Why is there a hidden skull in Holbein's The Ambassadors?

The skull is hidden because Holbein painted it using anamorphosis, a deliberately distorted projection that only looks right from one special viewpoint. In The Ambassadors (1533), two men, the French ambassador Jean de Dinteville and the bishop Georges de Selve, stand beside shelves crowded with globes, scientific instruments and books. Across the floor at their feet floats a strange grey diagonal smear. Look at the painting from an acute angle, from high on the right or low on the left, and the smear snaps into a human skull.

Why hide it? The skull is a memento mori, a reminder that everyone dies, however rich and learned. One simple explanation is that "memento mori" was de Dinteville's own motto. Some have imagined the painting hanging beside a staircase, so that people walking past would suddenly be confronted by death, although no suitable staircase has been found at de Dinteville's chateau. Another theory, from 1962, says the skull was meant to be viewed through a simple glass tube, which makes it look even more natural. That idea is reasonable but unproven.

Holbein hid other messages too: a lute with a broken string, a symbol of discord, and a crucifix half hidden behind the curtain. The same geometry that lets painters fake depth can also bend an image until it disappears, then bring it back for anyone standing in the right place.