This is an acorn of mass destruction. It’s stored in a small box with room for six but only containing the one.
A strange, mystical box, with many rumours attached, that does not want to reveal its secret…
Actually a real-world fungus, just heard about it. A fungus that tastes well and all, no ill effects. UNLESS you consume some beverage, even 3 (three) days after eating it. Then you become really sick, pains, vomiting, all the fancy stuff. Was really used to cure alcoholism. May be a joke or to make sure the heroes spend their time focused on the mission.