Book excerpt: Harley J. Spiller began collecting money at the age of five when, home sick from school, his father tossed him a sack of pennies and a Whitman coin folder. In the five decades since, author Spiller has amassed one of America's most extensive collections of unusual financial artifacts as well as a wealth of anecdotes and quirky historical details about U.S. currency. In Keep the Change, Spiller takes an irreverent look at our most uncommon coins and bills. Readers learn why greenbacks are green; what happens to worn-out bills (compost is involved); how artists navigate the fine line between art and mutilation; whether it's ever acceptable to burn money (short answer: maybe); and how coin clippers and counterfeiters through the ages have profited by manipulating money. This highly selective tour through currency legends and lore will inspire readers to look with a new sense of wonder at the bills that pass through our hands every day.