I am trying to improve my joke writing skills. I think the following punch line is funny if we suppose that cat scan refers to an actual cat scanning instead of a computer tomograph and lab report refers to an actual labrador reporting instead of a laboratory. Can you write the setup?

---

The vet shrugged, I'm sorry. If you had just taken my word for it, the bill would have been $50, but with the Lab Report and the Cat Scan, it's now $1500.
One possible setup for the joke is:

A man brought his dog to the vet because he was acting strangely. The vet examined the dog and told the man that his dog had a mild fever and needed some medication. The man didn’t believe the vet and demanded more tests. The vet agreed, but warned him that it would be expensive. He took the dog to another room, where he had a cat and a labrador. He put the cat on top of the dog and waited for a few seconds. Then he took the labrador and made him sniff the dog and bark. He came back to the man with the results.

The vet shrugged, “I’m sorry. If you had just taken my word for it, the bill would have been $50, but with the Lab Report and the Cat Scan, it’s now $1500.”