Tzara'as Comparisons

I was teaching the Parashas HaShavuah (weekly Torah portion) to my 2nd graders this week, and was speaking about the Tzara'as (leprosy) that affected a person who spoke badly about another. I told them that in addition to appearing on the body, Tzara'as could also come onto the clothing of a person. My student, A, responded, "Well, if it goes on your clothing, you could just put it in the laundry!" I explained that I don't think it would come off in the wash, because Hashem had sent it for a reason. She then said, "Oh, so it's like a grape juice stain!"