Probably in the carburetor

A man’s car stalled on a country road. When he got out to fix it, a cow came along and stopped beside him.
“Your trouble is probably in the carburetor,” said the cow.
Startled, the man jumped back and ran down the road until he met a farmer. He told the farmer his story.
“Was it a large red cow with a brown spot over the right eye?” asked the farmer.
“Yes, yes,” the man replied.
“Oh! I would not listen to Bessie,” said the farmer. “She does not know anything about cars.”

The postman

Visiting the Grand Canyon