Like Nannie's arm

This morning my son wanted breakfast.  When I asked him what it was he wanted for breakfast he stated yogurt.  Of course he always wants it when I don't have any left.  So imagine my feelings of good fortune when I opened the fridge and found we still had some.  I opened the container to find mold growing on it.  So I said "buddy we can't have any yogurt this morning there is mold on it".  His response "mold like on Nannie's arm?"  When I finally stopped laughing I had to explain that mold and mole are not the same thing.  OH BOY Y ME?