DPI 成语
	nigger in the woodpile|nigger|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.