Stomata are tiny adjustable pores on the surface of plants that balance gas exchange for photosynthesis with water loss. The mechanical interactions of a pair of cells, known as guard cells, are responsible for the reversible opening and closing of each pore, reliably regulating this dynamic process. Grasses, which inhabit dry environments, have evolved specialised stomatal complexes. Grass stomata consist of dumbbell shaped guard cells plus a pair of subsidiary cells, and this is thought to enable them to open and close more rapidly. We study the biomechanics of grass stomata through a combination of microscopy and Finite Element Method (FEM) modelling. We investigated the mechanical interactions of the guard cells with the subsidiary cells and elucidated the role that geometry, cell wall mechanical properties and cell-cell interactions play in the rapid opening and closing process of grass stomata. Our results are contrasted with a FEM model of a two-cell kidney shaped stomata, underscoring the unique properties present in grass stomata that enhance their performance. Overall, this research provides a deeper understanding of the interplay between cellular geometry and material properties for biomechanical mechanisms that enable efficient gas exchange in grasses.