User blog comment:IamJakuhoRaikoben/Chapter 400: Wings of Hope, Review./@comment-24066070-20140913200114/@comment-4933386-20140914022349

When Natsu was absorbing Atlas Flame's Flame, Atlas Flame felt like it was Igneel? That's probably the case, its probably because he actually felt Igneel biting/eating him.

Another thing I didn't get is how Grandeeney communicate with Igneel in the Fighting Festival arc(i can't remember which one).

My new theory is that the dragon slayers are like a portal that allows particular dragons(their respective dragon father) to come out from somewhere else.