ALT This video shows a killer T cell with fluorescently-labeled filamentous actin (orange) vigorously engaging a lymphoma cancer cell (blue). The T cell adheres to its target and forms a tight connection with active membrane protrusions projecting from the T cell/target interface. This robust actin cytoskeletal activity only occurs when a T cell identifies a valid target. The activity shown in this video is slightly slowed down from real time. We are only able to capture this dynamic actin cytoskeletal activity using a specialized microscope that can rapidly acquire 3-dimensional volumes called a Lattice Light Sheet microscope, which was developed in the lab of Eric Betzig at HHMI Janelia Research Campus. This data is was captured in collaboration with Wesley Legant, Bi-Chang Chen, and Liang Gao.