Incredible Visual Illusions (You won't believe your eyes!)
Incredible Visual Illusions (You won't believe your eyes!) by Al Seckel is a 2006 Psychology & Mind book written by TED speaker Al Seckel, paired here with the talk they gave.
An ambigram is a calligraphic composition of glyphs that can yield different meanings depending on the orientation of observation. Most ambigrams are visual palindromes that rely on some kind of symmetry, and they can often be interpreted as visual puns. Although the concept is older, the term "ambigram" was coined by Douglas Hofstadter in 1983–1984.