By attacking both routes the cats could then choose the easier of the routes and use the fixed ropes to go higher on the mountain. Winston suspected that a group of cats, being lighter of foot than humans, would have a better shot at traversing the ridge from the col. So he led Monster and Sherpa Pahu up to the col and the nearby snow hump for a better look. Indeed, the east face offered nothing but potential CATastrophe but the ridge itself was intriguing. It was sharp and corniced.
Cornices are where the snow piles up and reaches over the edges of the rock.
It is easy for the snow to break off and fall from the top, especially if weight is put on the cornice. Winston decided to set up camp IV below the snow hump in preparation for a traverse on the ridge. 3000 feet of essentially vertical snow. The going was slow and difficult but built in retractable crampons eliminated the need for the bulky ice tools that humans use and progress was steady. After two days fixed ropes stretched all the way to camp IVa, atop a bulge in the ice at over 20,000 feet and only a few hundred feet from the ridge.