Purple Foxx "How could you tell?"

A newly opened jar of marmite should have a pristine firm smooth level surface (except for maybe a tiny ring left by a burst bubble near the edge), and when you take some out the knife leaves a clear impression. The surface on the latest jar wasn't firm, it was more like discarded engine oil, and the impression left by the knife sank back to a vague but unsatisfying levelness so that you couldn't tell whether you were the first to use it or not.