A trap in the Vienna Gambit (I)

The Vienna Gambit (1.e4 e5 2.Nc3 Nf6 3.f4) was popular around the turn of the 20th century, but is rarely seen today. As such, it has the potential to surprise Black. By far Black's best response is 3...d5! One plausible but horrible response is 3...Nc6?, when 4.fxe5 Nxe5 5.d4 5...Nc6 (or 5...Ng6) 6.e5 gives White a position like the Halloween Gambit (1.e4 e5 2.Nf3 Nc6 3.Nc3 Nf6 4.Nxe5?! Nxe5 5.d4) without sacrificing a piece.

Another lemon is 3...exf4?, à la the King's Gambit Accepted. This is a different opening! 4.e5 is very strong for White, whether Black plays the immediate 4...Ng8 or 4...Qe7 5.Qe2 Ng8. Here are a couple of illustrative disasters: