A farmer comes home to find his sheepdog

A farmer comes home to find his sheepdog waiting for him.

The sheepdog says: “I herded the sheep into the barn, just like you asked!”

“You sure you got them all?” The farmer replies.

“Yep! All 40 of them!” Says the sheepdog.

“40? But I only have 37 sheep.” Replies the farmer.

The sheepdog answers: “I know. I rounded them up for you.”