This paper reports on the use of animation to enhance the observable range of choices in parametric rapid prototyping. Animation extends parametric rapid prototyping in three ways. First, it is used to reveal dynamically a set of possible forms from which to pick out one that may best serve a particular design project. That is, by animating the parameters that drive the geometrical model, we can visualize the continuum of alternatives that lie between specific key-framed settings of an architectural form. Second, animation can be used to pre-visualize a series of geometrical constructions for transforming a relatively raw three-dimensional form into one that satisfies the demands of a completed architectural project. Third, animation can be used to pre-visualize transformations of a given structure based on parameters set to adapt to varied conditions. In each case study, physical models were assembled through CNC fabrication.