A woman takes her dog to the vet. However, though she thinks it is sleeping, it is already actually dead.
The vet takes one look at the dog and says "Sorry to tell you but your dog isn't sleeping, he is dead."
The woman refuses to believe him and insists he carry out a test.
The vet goes into another room, and comes back with a cage.
In it is a cat. He lets the cat out, and it walks around the dog, sniffs, and goes back into its cage.
The vet tells the woman again "Look, your dog is definitely dead."
The woman asks "Ok, how much do I owe you?"
The vet replies "$500."
The woman, astounded by this high bill asks why the bill is so much.
The vet replies "$25 for me telling you your dog was dead and $475 for the cat scan."