  Background: We study mechanisms underlying the collective emotional behavior
of Bloggers by using the agent-based modeling and the parameters inferred from
the related empirical data.
  Methodology/Principal Findings: A bipartite network of emotional agents and
posts evolves through the addition of agents and their actions on posts. The
emotion state of an agent,quantified by the arousal and the valence, fluctuates
in time due to events on the connected posts, and in the moments of agent's
action it is transferred to a selected post. We claim that the indirect
communication of the emotion in the model rules, combined with the action-delay
time and the circadian rhythm extracted from the empirical data, can explain
the genesis of emotional bursts by users on popular Blogs and similar Web
portals. The model also identifies the parameters and how they influence the
course of the dynamics.
  Conclusions: The collective behavior is here recognized by the emergence of
communities on the network and the fractal time-series of their emotional
comments, powered by the negative emotion (critique). The evolving agents
communities leave characteristic patterns of the activity in the phase space of
the arousal--valence variables, where each segment represents a common emotion
described in psychology.
