Sheep walk about in fields, eating grass and plants. Controlling dozens of sheep in a field is not easy. It's a lot of running around. This is why farmers use sheepdogs.
Sheepdogs move big groups (called flocks) of sheep. First the dogs run around the field, pushing the sheep close together. Then the dogs force the flock to move.
The farmer tells the sheepdogs what to do by speaking to them. If the dogs are too far away to hear, the farmer uses whistles or hand signals.
Sheepdogs know more than 12 different commands. If the farmer wants the sheepdogs to collect all the sheep into one group, he says: 'Cast!' If he thinks a sheep is missing, he says 'Find!' and the dogs will go and look for the lost sheep.
'Come-bye!' means the dogs should move clockwise around the flock. 'Away!' means the dogs should move counterclockwise around the flock.
By following the farmer's instructions, the dogs can move the sheep anywhere he wants.