Yew tree berries (Taxus baccata). The red part of these berries, called the aril, is the only part of the yew tree that is not poisonous. The rest contains the heart-paralysing alkaloid taxine. Birds can eat the berries with impunity as the poisonous seeds pass through them undigested. They therefore disperse the seeds over wide areas, fertilising them with their faeces. Yews grow wild in woodlands throughout Europe.