This move is the point of White's opening idea: a pawn sacrifice to create weaknesses around the opponent's king. But now Black is not obliged to accept the gift.
1. e2e4  1... c7c6  2. d2d4  2... d7d5  3. e4e5  3... c8f5  4. g2g4 An ultra-aggressive option against the Caro-Kann Defense. 4... f5e4 [%c_effect e4;square;e4;type;GreatFind;persistent;true] The most accurate move, provoking the white pawn to f3. 5. f2f3  5... e4g6  6. h2h4  6... h7h5 