Watch the episode with the Juggernaut. Right before the mansion's sensors detect Juggernaut, Prof X and Wolverine are walking into the Danger Room. When the door to the Danger Room opens it shows a close up shot of the two and Wolverine's mask is off. It then shows an overhead view at an angle for a couple seconds and Wolverine's mask is on. Then it goes back to a close up view and his mask is off again!