nigger イディオム
housenigger
person who blindly follows simple-minded people, the term was used by Malcolm X. In slavery days, you had house slaves and field slaves. The house slaves were "well behaved" and were "rewarded" by being allowed to work in the "big house" close to the master. The field slaves were "rough" and only suited for field work. Thus the people were divided and pitted against themselves, instead of the common enemy
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.