Outside of a dog, a book is man's best friend.
Inside of a dog, it's too dark to read.
Source: From Journey in Word, ed. Cyndi Craven; an internet collection of quotations
-- Groucho Marx, (Oct 2 1890-1977), US comedian; He was the leader of the Marx brother team and famous for his ad-lib insults in his TV show You Bet Your Life, 1950-1961.