A virtual environment (VE) user's avatar may penetrate virtual objects. Some VE designers prevent visual interpenetration, assuming that prevention improves user experience. However, preventing visual avatar interpenetration causes a discrepancy between visual and proprioceptive cues. We investigated users' detection thresh-olds for visual interpenetration and visual-proprioceptive discrepancy and found that users are much less sensitive to visual-proprioceptive discrepancy than to visual interpenetration. We propose using this result to better deal with user penetration of virtual objects.