Neutrophils are amongst the fastest cells in our body, and their crossing of the intestinal epithelium into the mucosa, the origin of the pathogenic microbial threat, is a hallmark of mucosal function, and marks the active phase of many intestinal disorders. The migration of neutrophils is profoundly sensitive to the properties of mucus, and can be blocked in pathologically thickened mucus. The factors inside mucus that are responsible for this effect are unknown, but the mucin polymers, the basic building blocks of the mucus matrix, are important candidates, as they could impose geometrical constraints and provide binding sites both for the cells and for secreted molecules that regulate them. We study the role of mucins in neutrophil migration using the combination of a 3D mucus matrix and live tracking of cell migration. We ask: Does the mucin network provide substantial geometrical constraints to the cell? Do cells engage in strong interactions with the mucin fibers, or are the mucin fibers inert toward the cells? Do mucins regulate cell migration in the same way as other biopolymers, such as collagen or hyaluronan, or are fundamentally different mechanisms in play?