Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...d5

3... d5
This suspicious move allows 4.Nxe5 netting a pawn due to pin on the Nc6

'''1. e4 e5 2. Nf3 Nc6 3. Bb5 d5'''