Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nf6/3. Nxe5/3...Nxe4/4. Qe2/4...Qe7/5. Qxe4/5...d6

= Petrov's Defence, Damiano Variation =

5...d6
The only sensible response by black, as a follow-up 6. d4 is almost always played by white in an attempt to win a pawn.

Theory table
.

1. e4 e5 2. Nf3 Nf6 3. Nxe5 Nxe4 4. Qe2 Qe7 5. Qxe4