Let's recap what was shown in the tutorial rooms preceding this one: a chain won't straighten if it has slack (if it doesn't go from A to B in the minimum number of links), and an obstacle next to a diagonal chain link splits the chain into two parts that can each straighten separately if they meet all requirements.
Starting from the tail, the chain reaches (15,18) in the minimum number of links, but starting from (16,17) there is slack, so one obstacle is needed at (16,18) or (17,19). Then...
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×the chain is split in two, one starting at (15,18), and this gets to (25,12) in the minimum number of moves, but starting from (25,13) there is slack, so one obstacle is needed at (24,12) or (23,11). Then...
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×you need three obstacles in total, but you only have two! How can you get around this problem?
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×Might the floor markings provide a hint?
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×The head is facing NW, and we know (from 3N) that straightening happens when Beethro is ahead of the head, so if it's diagonal, he has to be further north or further west.
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×Beethro can be the third obstacle needed, if he is on exactly one specific tile.
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50th Skywatcher
