Petrov - Damiano variation
1. e4 e5 2. Nf3 Nf6 3. Nxe5 Nxe4
White advances the king's pawn to e4. Black plays the king's pawn to e5. White develops the knight to f3.
Black develops the knight to f6. White captures with the knight on e5. Black captures with the knight on e4.