In this article, we report on an experiment to monitor user attention in the serious game Le Village aux Oiseaux (The Birds’ Village). The primary motivation of this study was to explore the dynamic adaption of a game’s scenario and challenges to the skills of individual players. The solution we developed is a real-time, non-invasive visual attention monitoring method, based on the evaluation of reaction time within an open and continuous space. Our results contribute knowledge that can be useful for automatically managing individual game sessions. In addition, this knowledge can benefit game designers as well, helping them to improve gameplay, manage the difficulty of game environments, and optimize the positioning of visual resources on screen.