Ingore Normal Slope

This settings is important to get acquainted with. When this is checked the brush will ignore the curvature(normal) of the source mesh when painting, meaning it will affect all areas within the brush radius no matter if the curvature(normal) is very different from the brush center position. For instance when brushing a rabbit's ear this setting would brush both the back and front side of the ear. The setting will most likely be your rescuing angel when trying to groom areas like the inside of a characters mouth or in between the claws of and animal.

Ignore Normal Slope video: