Some climbers find it difficult to transition from face climbing to slab climbing. A big part of why this can be so difficult is, so far there is no indoor gym that offers this type of terrain to practice the technique before you get outdoors. So you basically have to get out there to try it, practice it, and master the skill.
If you notice above, legs are apart, right arm is up for balance, left arm is down for mantle, butt is sticking out for weight and to allow more shoe rubber contact with the wall.
There are some routes that have a variation of face and slab climbing. When there is such variation, it is sometimes difficult to switch your technique during your climb since one requires for your hips to be close to the wall and the other for your hips to be away from the wall.
Slab climbing is a type of rock climbing where the rock face is at an angle of less steep than vertical. It is characterized by balance- and friction-dependent moves on very small holds. Slab climbing – Wikipedia, the free encyclopedia
Face climbing is a type of climbing where climbers use features and irregularities in the rock such as finger pockets and edges to ascend a vertical rock face. Face climbing – Wikipedia, the free encyclopedia