Constructing causal mechanistic explanations is key in science. However, this often presents a challenge for students, as most mechanisms involve unobservable entity interactions. The human body can serve as a powerful tool to support mechanistic reasoning by enabling students to represent and investigate the actions of abstract entities with their bodies. In this instrumental case study, I demonstrate this assertion by showing how a pair of middle school students used hand gestures to represent the core mechanisms of air pressure and construct causal mechanistic explanations of the same. Students used a gesture-augmented simulation, using hand movements that symbolize pressure to control it. The use of these gestures prompts them to physically engage with the simulation in conceptually meaningful ways. By conducting a micro-genetic analysis of their speech and accompanying hand gestures, I show how the simulation’s control gesture helps them shift causal agency from non-scientific entities towards scientifically canonical entities. Additionally, I demonstrate how their collaborative use of hand gestures supports their dynamic and collective sensemaking about the concept, ultimately facilitating their mechanistic explanation of air pressure. Implications for instruction about gesturing, that can support mechanistic reasoning, follow.