I think the shield went by a column on the right hand side of the screen. The important part is what you do next: SPOILER
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Lean your shield against a column or statue. Lure the Gorgon to the shield by banging on the shield with your sword or, using a stone, tapping the column against which it is leaning. Stay hidden until the Gorgon is turned to stone by staring at the shield. Hurry up and decapitate the Gorgon before she regains consciousness.