"Well, sir/ma'am: Because I'm not Mary and my faith does not allow me to do so. It is spiritually unclean, but don't worry, I won't say any such thing to Mary, she has a right to her beliefs too. I am sure you as an employer would never want to discriminate on the basis of religion and cause an employee to fear losing a job or promotion because of their faith. In fact I am looking forward to earning my next promotion."