Interactive edge detection is used in both graphics art tools and in tools for building anatomical models from serially sectioned images. To build models, contours are traced and later triangulated. Contour tracing is time-consuming because of the fidelity and quantity of points needed, and expensive because of the background training required of individuals who do the tracing. Here we report extensions to interactive edge detection that reduce errors and effort. Our key contribution is a simple feedback interface called the leash, currently implemented as an extension to Intelligent Scissors, that lets the human user ‘lead’ the edge detection algorithm along a contour, but also helps the user to anticipate errors and provide immediate corrective feedback. Key words: Edge detection, 3d modeling, contour data, mixed-initiative computing, intelligent graphics, Intelligent Scissors