The Doctor

A doctor had just finished a marathon sex session with one of his patients. He was resting afterwards and was feeling a bit guilty because he thought it wasn't really ethical to have sex with one of his patients. However, a little voice in his head said "Lots of other doctors have sex with their patients, so it's not like you're the first..."
This made the doctor feel a little bit better until still another little voice in his head said,

"...but they probably weren't vets"