NIGGER IN THE WOODPILE

{n. phr.}, {slang} Something unexpected that changes a situation; a hidden factor or trick. - Racist and offensive, but commonly used in the past. * /I knew there had to be a nigger in the woodpile, because the man was being much too generous./ * /When the salesman gave him an extra tire for his bike, the boy suspected a nigger in the woodpile./