While chasing the horses over the prairie, Page 117 his horse stepped in a prairie dog's hole and fell.
(his horse; stepped; L:in a prairie dog's hole; T:While chasing the horses over the prairie) (his horse; fell; T:While chasing the horses over the prairie)
his horse his horse
stepped fell
L:in a prairie dog's hole T:While chasing the horses over the prairie
T:While chasing the horses over the prairie