The skill of a rock climber is shown by his choice of handhold and foothold, and his adhesion to those he has chosen. Much depends on a correct estimate of the firmness of the rock where weight is to be thrown upon it. Many loose rocks are quite firm enough to bear a person's weight, but experience is needed to know which can be trusted, and skill is required in transferring the weight to them without jerking. On rotten rocks the rope must be handled with special care, lest it should start loose stones on to the heads of those below. Similar care must be given to handholds and footholds, for the same reason. When a horizontal traverse has to be made across very difficult rocks, a dangerous situation may arise unless at both ends of the traverse there be firm positions. Mutual assistance on hard rocks takes all manner of forms: two, or even three, men climbing on one another's shoulders, or using for foothold an ice axe propped up by others. The great principle is that of co-operation, all the members of the party climbing with reference to the others, and not as independent units; each when moving must know what the man in front and the man behind are doing. After bad weather steep rocks are often found covered with a veneer of ice (verglas), which may even render them inaccessible. Crampons are useful on such occasions.
