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Although the human face is commonly used as a physiological biometric, very little work has been done to exploit the idiosyncrasies of facial motions for person identification. In this paper, we investigate the uniqueness and permanence of facial actions to determine whether these can be used as a behavioral biometric. Experiments are carried out using 3-D video data of participants performing a set of very short verbal and nonverbal facial actions. The data have been collected over long time intervals to assess the variability of the subjects' emotional and physical conditions. Quantitative evaluations are performed for both the identification and the verification problems; the results indicate that emotional expressions (e.g., smile and disgust) are not sufficiently reliable for identity recognition in real-life situations, whereas speech-related facial movements show promising potential.