Undertoe
Most evenings throughout the summer I go rock climbing or bouldering. Tonight it was bouldering, this means climbing boulders and there’s plenty of them where I live.The boulder problem I am trying in the photo is basically a traverse along a sloping edge, the edge is so sloping that it’s very hard to hang on it. It’s the old block on an inclined plane problem, as the angle of the incline is increased the block will slip, same with your hands on a sloping hold (sloper). One way of increasing the friction force is to increase the normal force between the hand and rock (as in the animation below). This could be done by getting a friend to press on your hands but that would be cheating. Alternatively you could pull down by placing a toe under an edge and applying an upward force. Newton 3 implies that a downward force will be experienced by the toe which in turn is transferred to the hand.
The boulder problem is called Undertoe.