We were taken to a sheep farm where a shepherd demonstrated to us how he used his collie dogs to round up the sheep. He used commands in both Gaelic and English as well as whistling to get the dogs to round up the sheep. One dog was blind but he sensed the sheep by their smell.
He used a command and the dogs went to fetch the sheep. Then he used another command to get the sheep to return. He could tell the dogs to move them to the left or to the right.