We and others have found it fruitful to assume that users, when interacting with spoken dialogue systems, perceive the systems and their actions metaphorically. Common metaphors include the human metaphor and the interface metaphor (cf. Edlund, Heldner, & Gustafson, 2006). In the interface metaphor, the spoken dialogue system is perceived as a machine interface – often but not always a computer interface. Speech is used to accomplish what would have otherwise been accomplished by some other means of input, such as a keyboard or a mouse. In the human metaphor, on the other hand, the computer is perceived as a creature (or even a person) with humanlike conversational abilities, and speech is not a substitute or one of many alternatives, but rather the primary means of communicating with this creature. We are aware that more “natural ” or human-like behaviour does not automatically make a spoken dialogue system “better ” (i.e. more efficient or more well-liked by its users). Indeed, we are quite convinced that the advantage (or disadvantage) of humanlike behaviour will be highly dependent on the application. However, a dialogue system that is coherent with a human metaphor may profit from a number of characteristics.