Thinning hair using a sliding movement with the blades of the shear partially opened to reduce volume and create movement is:

The technique described involves thinning hair while using a sliding motion with the shear blades partially opened, which is known as slithering. This method allows the stylist to progressively remove bulk from the hair while creating softness and movement. Slithering is particularly effective for producing layered looks or for removing weight without eliminating length, helping to add volume and texture to the hairstyle.

Other options, while related to haircutting, employ different methods. Slicing typically involves cutting hair at an angle to create texture and movement but does not emphasize the sliding motion as slithering does. Notching refers to making cuts into the hair to create dramatic texture and is not associated with the smooth, sliding technique. Beveling, on the other hand, involves cutting the ends of hair to create a rounded shape and often focuses more on the silhouette than on thinning hair or creating movement. Thus, slithering is the most appropriate term for this particular technique of reducing volume while maintaining a natural flow in the hairstyle.