Yak skiing is a sport practiced in the Indian hill resort of Manali as a tourist attraction.
The sport involves a skier waiting at the bottom of a slope and a yak at the top of the hill; yak and skier are connected by means of a rope going around a pulley at the top of the hill. To engage the yak, the skier must shake (and swiftly put down) a bucket of pony nuts. This attracts the yak, which charges downhill and pulls the skier upward by means of the rope.
References
Yak skiing Wikipedia(Text) CC BY-SA