The hissing breath cools the body and calms the mind.
Curl the tongue touching the roof of the mouth as far back as you can to the soft pallet. As you inhale clench the teeth together and slightly part the lips making a hissing "ssss" sound. Exhale through both nostrils. Repeat 5-10 times.
Use this pranayama only if there is obvious excess heat in the body. Do not use if the body feels cold, and practice with caution in wintertime.