Apple seeds
The seeds are mildly poisonous, containing Amygdalin.

Chocolate
Contains Theobromine at levels toxic to cats and dogs.

Deathberries
Deathberries are an extremely poisonous species of red berries, and are known to Twolegs as yew berries.

Holly Berries
Holly berries, while not as dangerous as deathberries, are still a danger to kits.

Foxglove seeds
Foxglove seeds are known to be a dangerous medicine. While they can help the heart, they can easily cause paralysis and heart failure. Can be mistaken for poppy seeds.

Nightshade
Twenty berries consumed can kill you, cause memory loss, or incapability of learning. Used to kill a cat who cannot be saved quickly, it is poisonous.

White Snakeroot
All parts are poisonous, causing nausea and vomiting.

Yew
Can be used to contract poison as a medicine, or causing to vomit if consumed.

Thanks for reading!