Holly berries can cause vomiting and diarrhea. They are especially dangerous in cases involving accidental consumption by children attracted to the bright red berries.[32] Ingestion of over 20 berries may be fatal to children.[31][32]
Holly leaves, if eaten, might cause diarrhea, nausea, vomiting, and stomach and intestinal problems.[32]
Holly plants might be toxic to pets and livestock.[33]
Holly berries are fermented and distilled to produce an eau de vie.[35][36]
From wiki
(Fruit brandy).
Ugh this just triggered memories of that scene from What Remains of Edith Finch (IYKYK).