Explain Huck and Tom's conscience dilemma?

Huck and Tom are in a dilemma because they know the truth and are afraid to tell it. Their consciences wear on them, particularly Tom, who begins having nightmares, stops playing with his friends, and sneaks food to Muff whenever he can. Fear of Injun Joe causes the boys to keep their secret. The question will be if their consciences will eventually win out.