Restriction: The monk must speak no words and attempt to be quiet in his actions.
Accidental noises and the sounds of battle (such as the sound of a fist
or weapon striking an opponent) do not affect his vow, though most monks
with this vow choose their weapons and opponents so as to minimize even
these sounds. The monk is allowed to make a nonvocal noise to warn
another of danger (such as by stomping or clapping). The monk is allowed
to use gestures and motions to communicate with others (including sign
language) and is allowed to write.
Benefit: A monk with this vow increases his ki pool by 1 ki point for every 6 monk levels (minimum +1).