This is called "Pugging," and the whole thing-trough, shaft, and knives-is a "pug mill."
"Diggers in the Earth"
Eva March Tappan
Thus, in South Africa you would talk only of "spooring," that is, following up the "spoor"; in India it would be following the "pugs," or "Pugging"; in America it is "trailing."
"Young Knights of the Empire"
Sir Robert Baden-Powell