A doctor had sex with one of his female patients and felt guilty all day long. No matter how much he tried to forget about it, he just couldn't. The guilt and sense of betrayal of his patient were overwhelming.

But every once in a while he'd hear an internal, reassuring voice in his head that said: "Don't worry about it. You aren't the first medical practitioner to have sex with one of his patients and you won't be the last. And you're single. Just let it go."

But, invariably, another voice in his head would bring him back to reality, whispering...
"You're a veterinarian, you sick bastard.