The main idea of this room is that the wubba considers various paths to Beethro, and rejects as invalid any paths that go over pit or wall. But it doesn't reject paths that go over monsters (in this case, the brains), and if its first choice move is into a monster, it gets stuck and won't move at all.
You have to take advantage of this by getting the wubba stuck in such a way that you can release it from a distance.
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Consider: wubba at 1, Beethro at 2 (easy to set up by blocking the wubba with Beethro's sword). Now Beethro steps SW to 3.
The wubba has two valid paths to Beethro that are both length 3 (via the SW and SE), and it prefers SW (see the list of directional preferences on the scroll). So SW is its first-choice move and it stays still. That gives Beethro just enough distance to move west and get the desired situation with the wubba on the SW pressure plate while Beethro is in the corner.
But if you try to do the same thing in mirror image with the other brain, when Beethro moves to the reflection of 3, the wubba still has two valid paths (SW and SE) and still prefers SW -- but now SW is its unblocked move, so it wriggles around the pits.
So a different strategy is needed to reach the SE brain:
Click here to view the secret text
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Wubba at 1, Beethro at 2. Beethro steps E and the wubba is stuck behind the brain.
The wubba doesn't move SW, even though it prefers SW to SE, because the path starting with a SE move is shorter. But Beethro can retreat and release the wubba from a distance by stepping over a diagonal line so that the wubba's SW and SE paths are equally short.
And again, if you mirror-image this and try to reach the SW brain this way, it won't work.
