Stunning decoys

(And no, we're not talking about carved wooden mallard ducks.) One final tactical example from Yakov Neistadt's Improve Your Chess Tactics (New in Chess, 2011): buy this book!

The legendary Nona Gaprindashvili missed an amazing shot in her 1979 game from the Soviet Championship with Irina Levitina. I'll quote from Neistadt's explanation, but I'll leave out the amazing move she missed.

Levitina-Gaprindashvili, Tbilisi 1979

White to play has to stop mate on g2 somehow....

Neistadt writes:

"Black has just played her queen to f3, to threaten mate.  In reply to 1.Qc6 (or 1.Qxe5+ Bf6 2.Qe4 Rfe8, Gaprindashvili's original calculations had gone 1...e4 and after 2.Qxe4 the decoy sacrifice 2...Rge8 3.Nxe8+ Rxe8.  But when the white queen appeared on c6, she realized that at the end of this variation, White in her turn can attack the queen with 4.Nd4

Levitina-Gaprindashvili, Tbilisi 1979

Analysis after 4.Nd4: Black to play

(4...Rxe4 5.Nxf3), and Gaprindashvili was forced to abandon her original intention.  Instead of 1...e4 she played 1...Qf5 and soon lost.

However, [...]"

So what did Nona miss?