See also: www.academia.edu/9964379/Schnarkverschlimmbesserung

In a 1910 edition of The Hunting of the Snark, an alledged error, which is not an error, had been removed. However, the removed white spot had a reason, as you see in the inset. The inset shows a segment from a 1876 edition with the white spot and a segment from The Bone Player (1856) by William Sidney Mount with a white spot (depicting a reflection from a glass).




[left]: Segment from an Illustration by Henry Holiday to Lewis Carroll's The Hunting of the Snark (1876).
[right, mirror view]: The Bone Player (1856) by William Sidney Mount, now displayed in MFA, Boston.