Flock Logic is an art and engineering project that explores how the feedback laws used to model flocking translate when applied by a group of dancers. The artistic goal is to create tools for choreography by leveraging dynamics of multiagent systems with designed feedback and interaction. The engineering goal is to develop insights and design principles for multi-agent systems, such as human crowds, animal groups and mobile robotic networks, by examining the connections between what individual dancers do and what emerges at the level of the group. We describe our methods to create dance and investigate collective motion. To illustrate, we analyze the overhead video of an experiment in which thirteen dancers moved according to simple rules of cohesion and repulsion in response to the relative position and motion of their neighbors. Importantly, because we have prescribed the interaction protocol, we can estimate from the tracked trajectories the time-varying graph that defines who is responding to whom as time evolves. We compute time-varying status of nodes in the graph and infer conditions under which certain individuals emerge as leaders.