Only and only if and only when always indicate necessary conditions. So this is actually telling us that in order for him to double dip his shrimp, it's a requirement that the cocktail sauce is down to its last bits. Required things go on the right. That's called the necessary condition, the required, the necessary thing. The contrapositive would say, if the sauce isn't down to its last bits, he's not going to double dip his shrimp. But we were just given a counter example.