Outside the cognitive psychologist’s laboratory, problem-solving is an activity that takes place in a rich web of interactions involving people and artefacts. This interactivity is constituted by fine-grained action extendash{}perception cycles, and it allows a reasoner’s comprehension of the problem to emerge from a coalition of internal and external resources. Taking an ecological approach to problem-solving, this paper introduces a qualitative method, Cognitive Event Analysis, for studying the fine-grained interactivity between a problem-solving agent and his/her environment. To demonstrate the potential of this method, it is used to study a single subject solving the so-called 17 Animals problem using a material model. The fine-grained procedure allows tracking the solution to a serendipity that was brought about because of the participant’s aesthetic considerations and a change in her perceptual figure-ground configuration. While a qualitative single-case method cannot prove specific models of problemsolving, it questions prevalent mentalist models, and it generates new hypotheses on insight problem-solving, because it allows the researcher to attend to outliers and to variability on a fast and fine-grained between-measurement timescale.