To suggest that the spire was planning how to kill them might be overstating its level of sentience...but maybe not.
Most of its victims were claimed on the downward half of their attempt.
The twins could see the accumulations of bodies at this side of the bottom of the pinnacle, so they knew they could not relax their caution.
As Feldspar had led the way up, so would Gypsum lead the way down, and both would be alert for the treachery they knew to be possible. They were helped by the impatience of the rock itself. Even as the first piton was driven, while Gypsum was still supported by the rope secured to his brother, who straddled the point of the pinnacle in a safe and stable position, the rock went soft. The pion sagged and almost fell out completely. Gypsum laughed and shook his head in amused surprise. Then he asked Feldspar to give him more rope. He dropped abruptly about ten feet and drove another piton deep into the spire. The rock held firm. The rope was threaded through the head and secured. A cautionary tug on the rope reassured him that the rock would not reject the metal and he glided down the rock face to a secure foothold several feet down. He signaled Feldspar and the older brother cautiously began his own descent. On the way down he paused to check the spot that had rejected his brother's piton. It seemed as hard and immutable as the rest of the rock. He shrugged and continued to follow Gypsum down the rock face.
More surprises were still to come.