We motivate an approach to evaluating the utility of life-like interface agents that is based on human eye movements rather than questionnaires. An eye tracker is employed to obtain quantitative evidence of a user's focus of attention. The salient feature of our evaluation strategy is that it allows us to measure important properties of a user's interaction experience on a moment-by-moment basis in addition to a cumulative (spatial) analysis of the user's areas of interest. We describe an empirical study in which we compare attending behavior of subjects watching the presentation of an apartment by three types of media; an animated agent, a text box, and speech only. The investigation of users' eye movements reveals that agent behavior may trigger natural and social interaction behavior of human users. Copyright 2005 ACM.