nigger in the woodpile

[nigger in the woodpile] {n. phr.}, {slang} Something unexpectedthat changes a situation; a hidden factor or trick. - Racist andoffensive, but commonly used in the past.

I knew there had to be anigger in the woodpile, because the man was being much too generous.

When the salesman gave him an extra tire for his bike, the boysuspected a nigger in the woodpile.