Refutation right on the spot

I have always been impressed by stories of Grandmasters who, upon being confronted by a new or surprising idea in the opening, think hard and come up with a refutation right on the spot.

In club play, you may find the right idea, and not even realize it until it is too late. If then.

perrypawnpusher - KnightIsHorse
blitz, FICS, 2011

1.e4 e5 2.Nf3 Nf6 3.Nc3 Nc6 4.Bc4 Bc5

The Italian Four Knights Game, about to become the Italian Four Knights Jerome Gambit.

5.Bxf7+ Kxf7 6.Nxe5+ Nxe5 7.d4

7...Bb4

This defense can work for Black, but he needs to give some thought as to what his plan will be.

8.dxe5 Bxc3+ 9.bxc3

Now, retreating the Knight, or even letting it expire on f6 with 9...Re8 10.exf6 Rxe4+ 11.Be3 Qxf6, keeps an edge for Black. 

9...Nxe4 10.Qd5+

Black resigned

It was possible to continue, as in my most recent example, perrypawnpusher - Aerandir, blitz, FICS, 2011, but I suspect that KnightIsHorse was discouraged by the turn of events.