Hmong Ritual in Laos

Just back from Laos where I had the good luck to wander into a Hmong village during a string tying ceremony led by a village shaman. I had rented a motorbike and was going around the countryside and during a brief rest under some shade was invited into a hut to take part in, and photograph the ceremony being held for a sick 3 month baby boy named Khang Vu. My very basic understanding of the ritual is that it is peformed to call the ancestral spirits with food, drink and gifts to the celebration and to implore their aid toward the good health and fortune of the sick relative and for the family and village.