Chess is 99% Tactics

It's an old chess adage, but it's probably a slight exaggeration. Certainly tactics can be much more important than position, and many "won" games have been lost due to tactics. Nowhere is the adage more true than at the junior level. Grandmasters may preside over drawn-out positional wins, but the rest of us are far more likely to find (or fall victim to) tactical shortcuts.

In the position below from my 5th round game at the Wisconsin Closed Championships this past Labor Day, my opponent (playing white) stumbled into a tactic that shortened the game considerably. Can you spot the win for black?

Black to move...

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White has just recaptured a pawn on g3. In this position, black has a strong advantage thanks to his extra pawn and protected passed pawn on d4. But the game ended in just a few moves. What tactical shot did black find here to decide the game immediately?