Why do O'Reilly books have animals on their covers?
Edie Freedman, who designed the first O'Reilly programming
books' animal covers, said she was inspired by the weird buzzwords
used by UNIX programmers, many of which were the topic of the
books. She therefore looked for images of 'Dungeons and Dragons'
images, and came across a collection of 19th century animal wood
engravings, which she figured would fit the buzzwords. Please see
the full story in the related link.