In this exploratory study, we investigate the potentiality of comparing mathematics and physics, from generic characterizations to interdisciplinary tasks and textbook analysis, as opportunities to foster secondary mathematics preservice teachers' awareness of the epistemic core of such disciplines. We designed and implemented a teaching sequence with Italian master students with a mathematical background, relying on a framework developed within a project about interdisciplinarity in preservice teacher education (IDENTITIES), and carried out three case studies analyzing data collected. We discuss the impact on students' conceptions and the development of learning processes at the boundary that our teaching sequence might have, as well as further reflections on how to make our activities more effective.