Answer: The berries of holly are poisonous if eaten in quantity. (As with any potentially poisonous substance, the does makes the poison.) Berries contain saponin toxins which in themselves may produce vomiting, abdominal pain, and in some cases diarrhea. It's not likely that a dog will ingest the berries, but a curious child might.
According the AMA Book of Poisonous Plants, if holly berries are ingested, "induce vomiting and follow procedures to delay absorption and speed elimination".
In order to produce berries, you'll need a female and a male plant. Unless berries are an important consideration in your landscape plants, you can avoid potential problems by using only male plants in your yard.
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