The Caro-Kann (1.e4 c6) is an annoying opening to play against; White gets only a small edge, if that. The trap below is essential to know if you play either side of the Caro-Kann. It can win you a lot of points as White. Those who play the 2.d4 d5 3.Nc3 dxe4 4.Nxe4 Bf5 line will often blithely play 4...Bf5 against the Two Knights Variation (2.Nc3 d5 3.Nf3) as well, erroneously thinking that there is no significant difference between the two lines.
Black should avoid this trap by playing ...Bg4 on move 3, 4, or even 5, or by playing 4...Nd7 or 4...Nf6, with a likely transposition to standard variations. On move 7, 7...Qd6! (Mayka-NN, c. 1975) is the best try. After 7...Bh7?, Lasker's 8.Qh5! forced 8...g6, leaving Black's bishop looking horrible on h7. His 9.Bc4 again threatened mate, making 9...gxh5?? impossible. Note that 9...Qxd2+ 10.Bxd2 gxh5 would avoid mate, but lose material to 11.Nxf7 or 11.Bxf7+. After 10.Qe2, Black should have played 10...Qe7! guarding f7, when Black has an ugly position but can still play on. 10...Be7 may also be possible. After 10...Bg7?? 11.Nxf7!, Black resigned in light of 11...Kxf7 12.Qxe6+ Kf8 13.Qf7#. Note that 10...Nf6?? (Alekhine-Bruce, Plymouth 1938) and 10...Nd7?? (McKenna-Stockinger, 1994) are met the same way.
Twenty-six years later, Lasker improved on his own play with 9.Qf3! (winning at least a pawn by force) Nf6 (9...Qd5?? 10.Qxd5 cxd5 11.Bb5+ Nc6 12.Nxc6 a6 13.Ba4 1-0 Tartakower-Ellinger, Horsington 1944) 10.Qb3! Qd5 11.Qxb7! Qxe5+ 12.Bxe2 Qd6 (White threatened Qc8#) 13.Qxa8 Qc7 14.a4! Bg7 15.Ra3 0-0 16.Rb3 and White won in Lasker-Müller, Zurich 1934.