A computer animation demonstrates the flexible dynamics -- the moving parts -- of human IgG antibody. Three-dimensional images of two individual antibody particles (gray) were generated using EM tomography with IPET. The demonstration shows how the same molecular chains (red, orange, and green noodle-like models) of antibody particle No. 1 can fit precisely into particle No. 2, which was found under the microscope in an entirely different pose.