It's not *really* a bug - it's quite consistent with how giants work. Though if we wanted to change it... well, one moment first.
We're back down to brained movement preferences here. After Beethro moves, we need to see which part of the Rock Giant will be controlling the move. This is always the closest corner of the giant. In your example hold, this would be the SE corner after Beethro moves E.
The *obvious* move is S. However, Beethro's sword blocks that move. That means that the SE part of the giant can't move directly into the square that's 0 distance away from Beethro.
That leaves tiles that are 1 distance away from Beethro. The available squares in that case would be W, SW, SE and E. SW is blocked by Beethro's sword, W is blocked on the first turn by the wall, and E and SE are open.
Brain movement preferences prefer E to SE if they're the same distance from Beethro. The giant doesn't understand that one of its *other* parts would kill Beethro if it moved SE. (In fact, it never understands this - the only reason an unbrained Rock Giant does this is due to Flanking movement preferences). So it moves E.
As you continue moving E, the brain movement preferences will next prefer a W movement to E, pulling the giant one more move back before it follows the rest to the E. All this is standard brain movement... just mapped to the Rock Giant's unique shape.
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If we wanted this changed, we'd likely want to add a killing move detector for both unbrained and brained Rock Giants, similar to how other monsters already prioritise killing moves. But otherwise, it's pretty consistent with normal brain preferences, just with a different shape.
EDIT: By the way, such a change *would* mean something to unbrained giants as well. Consider this example:
....
.GG. G = Rock Giant
.GG. B = Beethro on NE-facing arrow
..B.
....
In the example, the Rock Giant cannot move S to directly kill Beethro. Flanking kicks in, so the Rock Giant must now choose between SW and SE. Both are actually open, but the Rock Giant prefers SW movements and will pick this one, even though a SE movement would actually kill Beethro.
If you placed Beethro's sword to the W, the SW movement would also be blocked and force the Giant to the SE, killing Beethro. If a Rock Giant checked for killing movements first, this would not be necessary. So it's up to debate whether such a change should be implemented.
[Last edited by TFMurphy at 02-01-2008 05:31 AM]