The use of motion pictures for research has a long history, of course, but beyond documenting a phenomenon and then projecting it for demonstration, scientists using this technology spent much energy figuring out how to extract information from a strip of film. Understanding film (or audiovisual) analysis is therefore necessary to grasping the relationship between an object of study, moving-image technology, and scientific evidence. This article explores one common technique within that history of film analysis: projecting a frame of the (...) motion picture and then tracing the object of study onto paper, which was especially important for behavioral sciences such as developmental psychology or ethology. Behavior became tangible through a variety of means, but for those who relied on film for their observations, such as developmental psychologist Arnold Gesell, behavior took form at least partly through the process of tracing. Gesell's use of this technique reveals the broader functions of tracing as well as the patterns that emerge from its interplay with other inscriptions in the creation of evidence. How does behavior take form? The practice of tracing provides one answer to this larger question. (shrink)