Petroff's Defence (or the Russian Game) arises after:
1. e4 e5
2. Nf3 Nf6
There is an interesting trap where white may blunder his Queen away early in the game after:
3. Nxe5 Qe7
4. Nf3 Nxe4
5. Nc3?? Leads to Nxc3+, and black will win a Queen and a Knight for a Knight.