Since 3...cxb4 4.Rxb4 is hopeless for Black, Spassky tries a counterattack.
4.exf5?! e4 5.Bd2 exf3+ 6.Bxf3 gxf5 , when the connected pawns and the strong bishop on g7 yield Black some slight compensation for the piece.
A decisive queen transfer with two concrete ideas: 2 R(Q)h3 with mating motifs, and 2 Qg2, creating deadly threats at g7 and g8.