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e f g 1 h Why it works
A trap in the Advance Variation of the French. White plays 6.Bd3 (the Milner-Barry gambit idea). The d4 square is attacked twice (by the c6 knight and the b6 queen) and defended once (by the f3 knight), so 7...Nxd4?? looks like winning a pawn: 8.Nxd4 Qxd4 'regains' the piece while attacking the d4 knight. But there follows 9.Bb5+! — a fork of king and queen: 9...Bd7 10.Bxd7+ Kxd7 11.Qxd4, and White wins the queen. The mistake is move-order: Black captured on d4 before developing the bishop to d7. Game Martinez — Rybansky (World U10, 1993).
Refutation
7...Bd7! — the correct move, the whole point of the line. The d7 bishop pre-covers b5, and only now can Black capture: 8.O-O Nxd4 9.Nxd4 Qxd4 — after 10.Bb5 there is 10...Bxb5, no fork. Without this preparatory move, capturing on d4 loses the queen.