In a discussion about the contents of dining casters, it is noted that two of them held salt and pepper, while the third's contents remain uncertain. Although it is commonly assumed that the third caster contained dried mustard, this assumption is largely based on a lack of other plausible options. Food historian Gerard Brett highlights that there has never been a satisfactory alternative proposed, indicating a gap in historical evidence regarding mustard's popularity as a readily available condiment.

As time progressed, particularly by the era of Mr. Marsham, the third caster's role began to fade away. The lack of evidence supporting the frequent use of mustard by diners may explain this decline. The mystery surrounding the actual contents of the third caster reflects broader themes in dining history, demonstrating how transient food preferences can be and how certain food items can become overlooked or forgotten over time.