In Virtual Reality, the need to understand how subjects perceive their representation is gaining attention and importance. We present a contribution to a better understanding of the sense of embodiment by assessing two of its main components, body ownership and agency, through an experiment involving alien motion. The key aspect of the experimental protocol is to integrate a condition with some personalized alien finger movement while the subject is asked to remain still. Body ownership appears to be significantly reduced, but not agency. We also propose a metric to assess quantitatively that the view of the alien movement induces more finger posture variation compared to the reference context in the still condition.