Towards the end of the movie, when the X-Men go into the underground lab, Nightcrawler and Storm go to save the mutant children who are being held captive in an submerged cell in the floor. Nightcrawler teleports into the cell, but just before he goes down, there is a shot of the children calling for help. If you look in the shadows, where Nightcrawler will eventually emerge from, his silouhette can be seen already in the cell...before he ever leaves the area above the cell.