We report on The Manual Input Sessions, a series of audiovisual vignettes which probe the expressive possibilities of free-form hand gestures. Performed on a hybrid projection system which combines a traditional analog overhead projector and a digital PC video projector, our vision-based software instruments generate dynamic sounds and graphics solely in response to the forms and movements of the silhouette contours of the user's hands. Interactions and audiovisual mappings which make use of both positive (exterior) and negative (interior) contours are discussed.