Got bad joints? So do most computer models of the human body, because they neglect nuances of anatomy and physics. That can make animated characters look fake -- or worse, make virtual surgeries and digital crash-test dummies inaccurate. Now computer scientists have developed software that more realistically simulates the complex movements of human joints. Victor Ng-Thow-Hing at Honda Research Institute USA in Mountain View, CA, and New York University's Wei Shao model the human shoulder, for instance, as four separate joints instead of just one. Specify the geometry of the upper arm, collarbone, scapula, and rib cage, and the computer does the math to figure out how they all interact when, say, a virtual athlete throws a ball. A graphical interface lets animators and other users add layers of complexity to each joint to produce more detailed behaviors, such as bones slipping with respect to each other. Video game developers have expressed interest, says Ng-Thow-Hing, but biomedical applications are still a few years away.