Open a book to study or read, as in He passed the exam without cracking a book. This expression employs the verb to crack in the sense of “to open,” a slang usage that dates from the early 1700s. [Colloquial; c. 1930]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.