Lesson
White to move. Main line: 1. d4 e5 2. dxe5 Nc6 3. Nf3 Qe7 4. Bf4 Qb4+ 5. Bd2 Qxb2 6. Bc3 Bb4 7. Qd2 Bxc3 8. Qxc3 Qc1#
After 4.Bf4? Qb4+ 5.Bd2 Qxb2 the queen is deep in White’s camp. 6.Bc3 Bb4! pins the bishop to the king, and once the pieces come off with 7.Qd2 Bxc3 8.Qxc3, the fatal 8...Qc1# arrives — the king is boxed on e1 by its own pieces and the untouched e2/f2 pawns.
The trap only springs if White plays the natural-but-loose 4.Bf4 and 6.Bc3. It is a sharp reminder that even against an unsound gambit, you must watch your own back rank and the b2-square before grabbing material.