Oleander (Nerium oleander)

Don't hate it because it's beautiful; hate it because it's poisonous. Giving a bad name to pretty flowering shrubs everywhere, oleander is extremely toxic. As little as one leaf may be enough to kill a child or a curious house cat. Luckily, most grown humans don't make a habit out of gnawing on the shrubbery. Good thing, since the toxins in oleander cause a whole range of severely unpleasant symptoms, including nausea, diarrhea, blurred vision, dizziness, disorientation, seeing halos, low blood pressure, an irregular heartbeat and, of course, death.