How does one thin a light, short beard? And is it sufficient to close the palm and pass the fingers over it, or must it be with the full palm?

The light beard must be run through (خلله) so that water reaches the skin. This is done by placing a handful of water from underneath it with interlaced fingers, or from its sides, and rubbing it. This is based on the Hadith (definition) of Anas, raised (to the Prophet): "When he performed ablution, he would take a handful of water and place it under his chin and run it through his beard, saying: 'Thus has my Lord commanded me.'"