This paper discusses the modeling, the observation, and the analysis of a social experiment, in which we built an online social network to observe interactions between people. We try to model the problem from the micro-economics aspect; we use the concept of utility to model people's behaviors in this experiment. Furthermore, we consider incentive reward as an external factor and observed how people's behavior would change based on how we give incentive reward. We assumed the scenario of content recommendation in an online social network and compared the two reward assignment rules: i) a user gets reward if she or he informs her/his friend of the pointer to the content and ii) a user gets reward if her/his friend she or he informed of the content pointer reacts to the content. We expect that, in the former, the social network is not activated because the information flow is unidirectional, while, in the latter, the social network can be activated because it stimulates people to react to the information they have received.