Queen Sac Leading to Knight Fork

The following tactical chess position arises rather early in a game where Black essayed a French Defense. Avila from Guam playing at ICC confidently plays d4 in a position where he appears to stand much better. He has two pieces out compared to Black's what appears to be offside Knight at b4.

Veteran chess players know that there are always exceptions to general rules. What is the exception to the rule that claims the better developed player should have an initiative in the diagrammed position?

Put another way, what move should Black play to gain a lasting initiative which should eventually win the game for him?  Hint: The title of this post completely gives it away!