Sak Yant is an Ancient magical practice of tattooing Sacred Geometry, using Buddhist,Brahman and Animist imagery and magical incantations (Kata), written in Khom (Ancient script used to write Pali Sanskrit).
Sak means “to tap [tattoo]“, and yant, derived from the Sanskrit word yantra, means “sacred geometrical design.”
Sak yant designs are normally tattooed by wicha (magic) practitioners and Buddhist monks, traditionally with a long bamboo stick sharpened to a point (called a mai sak) or alternatively with a long metal spike (called a khem sak).
What does it have to do with barefooting?
If the monk who does the tattoo works alone, he uses his barefeet to stretch the skin. This video shoes the foot stretch action.
A shod person wouldn’t be able to create such mystical tattoos. His or her feet are much too weak and inflexible to accomplish such magical feats ; ).