So look for a space where you can arrange for the snake to be somewhere that all 4 of its moves are blocked.
×The north and east sides are no good, because the scrolls and pits make a flat wall. The mimic potion is no use because it's out in the open.
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×But there are some spots on the SW diagonal border where you can trap the snake if you close the door on it at the right moment. Like these:
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×Click here to view the secret text
×Wait until the snake head is on one of those spots, then strike the orb to trap it.