Priori Incantatem

On the day of the third task, Harry was transported to Tom Riddle’s (Sr.) grave. There he witnessed the rebirth of his bitter foe and nemesis Lord Voldemort. Voldy, perhaps the greatest Dark Wizard to be born for centuries had plans in full flow to end ‘The Chosen One’. His duel with Harry looked as if it was the end of the ‘The Boy Who Lived’. But, here again JK surprised us all with her unique and highly innovative brain and cool logic. She introduced a new phenomenon- ‘Priori Incantatem’ or the reverse spell effect. Later Dumbledore tells us the crux of this phenomenon- It happens when a wand meets its brother. Both the wands do not work properly against each other. If however, the owners of the wands force them to battle, a very rare effect takes place. One of the wands will force the other to regurgitate spells it has performed–in reverse.
D’s words can be counted for on that night when the spells were fired, both the wands started vibrating and a narrow beam of golden light connected them. Both Harry and Voldy were lifted off the ground and Harry survived. Though, one thing has intrigued me often. D said that one and only one wand will force the other to regurgitate spell. So why was it that Harry’s wand forced Voldy’s wand even though Voldy is a much more powerful wizard than Harry? Why not vice-versa? Is there something more to it that even old D does not know? I would now like all to see this piece of interview of JK...

Sarah Wallace for the Irish Independent - How did you think of the bond between Harry and Lord Voldemort?
JK Rowling: That is another one of those questions that goes right to the heart of the series. I can't answer. It touches way too closely on book 7. Sorry. Good question.

Does it not give us a clue that there is something more than told or even imagined. I have a theory that when Priori Incantatem takes place, then maybe the creature from which the core was made gets alerted and there is an invisible connection between the three(2 wands and the creature). The creature can then decide that which wand will force the other. As we know that Harry’s wand forced Voldy’s wand, so I believe that Fawkes had at that night interfered in the duel and decided the fate of our Hero. If so, doesn’t it seem that she has a very important role to play in Book-7 and is not dead as thought by Harry.
One thing is for sure , she isn’t merely a songbird. Final piece of Interview to support my theory-Peter Humphreys for BBC Newsround. - Who did Fawkes previously belong to and will he play a vital role in the next book?
JK Rowling: I am not going to answer about the role in the next books, which probably gives you a big clue, and he has never been owned by anyone but Dumbledore. You will notice that when Harry goes back in the Pensieve in this book, Fawkes is never there, and ­­ no, I am sorry, not in this book, I take that back. When Harry has previously seen the study with a different headmaster he saw it with Dippet and Fawkes was not there then. Fawkes is Dumbledore's possession, not a Hogwarts possession. I believe it has also answered the question(particularly Andros) if Fawkes belonged to some other person.