The paper looks at different roles of physical objects in supporting design thinking and communication, i.e. object as starting point, as communication medium, episodic memory trigger, etc. Still, what I found to be the most interesting part of the paper was the comparison it made between sketches and CAD models. CAD models try to minimize the ambiguity in representation so that parts can be produced based on the models without errors. Hence, CAD system are not supporting the fluid process of idea developmet. Whereas sketches are ambiguous, which might lead to new ideas in the development phase of the product. In addition, when designers watch each other sketch they are able to focus on the detail that is been drawn at the moment, and not on the entire product or component at once. That helps focus the design communication around the same feature. The authors suggest that prototypes (physical objects) should be used in designing tangible interfaces, but one should be aware of the level of the ambiguity in the prototype.