Continuing with the theme of unexpected queen checks, after 1.e4 c5 2.Nf3 e6 3.d4 cxd4 4.Nxd4 a6 (the Kan Sicilian), White can play almost anything: 5.Nc3, 5.c4, 5.Bd3, 5.Be2, 5.Be3, 5.g3, etc. Er, almost anything except 5.Bf4??, that is. Black wins a piece with 5...e5! (forking bishop and knight) 6.Bxe5 Qa5+ (forking king and bishop), winning the bishop.