Whenever Nightcrawler is in his "human" form, his index and middle fingers are always shown "connected" as are his ring and pinky fingers. This is to show that he still has only three fingers under his holographic inducer. However when Scott and Kurt are discussing the possibility of Amanda asking Kurt to the dance, he crosses his index and middle fingers--something he shouldn't be able to do since they're technically the same finger underneath the holo inducer.