Chametz that is also terumah (or terumah that is also chametz) - what happens when it is misused? Which is to say, violating a prohibition and also incurring damages. Which will be a different value if the terumah is pure or impure. Also: One who is not a kohen who eats a k'zayit's amount of terumah has to pay back the amount and then a fifth of the total value on top of that. Though Abba Shaul disagrees, and the question is what is the crux of the disagreement.