A few years ago, three [actually only two] separate books were discovered in Harvard University’s library that had particularly strange-looking leather covers. Upon further inspection, it was discovered that the smooth binding was actually human flesh.
[T]he practice of using human skin to bind books was actually pretty popular during the 17th century. It’s referred to as Anthropodermic bibliopegy and proved pretty common when it came to anatomical textbooks. Medical professionals would often use the flesh of cadavers they’d dissected during their research.