One plant that many home and pet owners have in their yards and are unaware of the highly toxic effects it may have is the Sago Palm. It is the nice ornamental bushy palm at the corner of the house or near your pool. Many people are unaware of the highly toxic dangers it holds.
The whole plant of the Sago Palm has a toxin called Cycasin and dogs really enjoy chewing on the fronds and the berries . The berries are the most toxic and may only take a couple to cause toxicity. Toxic affects causes liver damage, gastrointestinal discomfort, jaundice ( yellowing of skin), blood not able to clot, vomiting, melena (blood in the stool), increased thirst, hemorrhagic gastroenteritis, bruising, liver failure, and even death. If you suspect your pet possibly ingested this plant take them to the Veterinarian or Emergency clinic immediately.

When symptoms are maintained and the pet can eat and drink on its own without vomiting. The pet is sent home on SAM-E, milk thistle and sometimes antibiotics to help the liver recover from its insult. Bloodwork is rechecked in 3-4 weeks to monitor liver values.
Oleander: has a cardiac glycoside very similar to digoxin throughout the entire plant. When ingested it can cause nausea, stomach cramping, cardiac arrhythmias, coma and even death.
http://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants