This jack knife was once used by the donor’s father on Shabbat to cut the challah. This type of knife, where the blade could be tucked into its case and thus hidden during the grace after meals, was the preferred type of knife for Sabbath meals by many Eastern European Jews because it was preferable not to have a blade on the table during the after dinner prayers. One interpretation for this concept is based on the story of a man who was reciting grace after having eaten dinner when he became so distressed by the thought of the destruction of the Temple while reciting a prayer asking God to restore the destroyed Temple and the city of Jerusalem; that he stabbed himself with a knife left out on the table. Another explanation for the removal or covering of any blades is that the meal table is comparable to the Altar in the Temple that once stood in Jerusalem and just as the use of iron tools to cleave the stones for the Alter is prohibited, metal knives are prohibited while saying grace after meals.
Jackknife for Sabbath Hallah with mother-of-pearl inlay, Collection of Yeshiva University Museum, Gift of Sylvia Axelrod Herskowitz