Final answer:
The two prisoners assist in the hanging because of a dilemma they face in the prisoner's dilemma scenario, and it suggests that their humanity is influenced by the incentives and consequences they face.
Step-by-step explanation:
The situation you are describing is known as the prisoner's dilemma, which is a concept in game theory commonly used in social studies. In this scenario, the two prisoners assist the guards in hanging the third prisoner because they face a dilemma between cooperating and betraying each other. If both prisoners remain silent and cooperate, they would only serve a total of four years in jail. However, if one prisoner confesses or betrays the other, they can potentially get a lighter sentence. This suggests that the prisoners' humanity is influenced by the incentives and consequences they face, leading to a difficult decision where they prioritize their own self-interest over their solidarity as prisoners.