Howard was feeling guilty all day long. No matter how much he tried to forget about it, he couldn't. The guilt and sense of betrayal was overwhelming.
Every once in a while he'd hear a soothing voice trying to reassure him - "Howard, don't worry about it. You aren't the first doctor to sleep with one of his patients and you won't be the last."
But invariably the other voice would bring him back to reality - "Howard, you're a veterinarian."