As with any marine life, you should respect thanks is a wild animal. That being said, I have never encountered an aggressive moray (have never given them an excuse to be either). You will often see morays opening and closing their mouth, which looks like they are ready to attack at any moment - in reality, they are forcing water over their gills while stationary. In areas when divers routinely feed speared lion fish, I have also seen large morays come out and follow the group, just in case there is a free meal in it for them. Again, not aggressive - just curious.