Chess Opening Theory/1. e4/1...e5/2. f4/2...exf4/3. Nf3/3...g5/4. h4/4...g4/5. Ne5/5...d6/6. Nxg4

6...Nf6 is the usual move. Black aims to come out with a lead in development after an exchange of knights on f6, that will compensate for her suspect kingside pawn structure.

6...Be7 is a move that lay gathering dust on a shelf for a century and a half, between Howard Staunton losing a famous game with it against Baron Tassilo von Heydebrand und der Lasa in 1853 and the computers rediscovering it in the 1990s. It's had a very positive score from a small sample size. Black threatens to take White's pawn on h4, because taking pawns means you have more of them than your opponent does.