They knew they must use extra caution on this ascent. They did so. Feldspar was meticulous about driving the pitons, both in placement and depth. He chose his hand and foot holds carefully, testing each one before daring to put even half his weight upon it. Gypsum was extra careful to secure the rope between them to the pitons and wait until his brother was well established in a new position before moving himself.
The most dangerous enemy is the one you do not recognize.
Feldspar reached up and grasped an obvious and convenient knob of rock. He pulled on it, testing it carefully. It was strong, and he pulled himself up. The knob responded with strong stability. The twin lifted his right foot off its resting place to set it upon its new foothold.
The knob of rock came off in his hand and he skidded down the rock face in an uncontrolled slide, grasping uselessly at nonexistent handholds as he fell past his brother.
Gypsum braced himself and tightened his grip on the rope. Feldspar quickly reached the end of the rope and hung, helpless, his fate in the hands of his brother.
With help he was soon re-established on the rock face with a secure foothold and a firm handhold. He waited a few minutes for his heart to slow before attempting to continue the climb.
But they had not yet discovered the true danger of this particular spire.