Search and capture in space and time How immunological T cells scan target cells for ligands is poorly understood. Cai et al. examined microvillar dynamics in living T cells in three dimensions and real time. The T cells palpated all spots on a surface within about 1 min through rapid movements of their microvilli. The time it took to scan the surface matched the movement rate of cells through tissues. These contacts took place in the absence of T cell receptor recognition and were stabilized independently of signaling or the cytoskeleton. Instead, stabilization depended on ligand affinity. The findings explain why many of the previously described components of the immunological synapse and T cell receptor signaling reside on three-dimensional microvillar-derived projections. Science , this issue p. eaal3118