Gardeners plant mums to keep rabbits away. Guess what?
 The flower heads are somewhat toxic to humans too. But not terribly.
 Touching them can make you itch and puff up a bit.
 

 
Oleander

Oleander is one of the most poisonous plants and contains numerous toxic compounds,
many of which can be deadly to people, especially young children.

Lily of the valley

A little bit of Lily-of-the-valley (Convallaria majalis) probably won't hurt much,but if you eat a lot,
you'll probably experience nausea, vomiting, pain in the mouth, abdominal pain,
diarrhea and cramps.Your heart rate might also become slow or irregular.

Ficus

Rhododendron

Some species are poisonous to grazing animals.
These Rhododendrons have a toxin called grayanotoxin in their pollen and nectar.
People have been known to become ill from eating honey made by bees feeding on rhododendron and azalea flowers.

 Narcis

All Narcissus varieties contain the alkaloid poison lycorine, mostly in the bulb but also in the leaves.
 

 
Ricinus communis (castor bean)

The seeds of castor bean or castor oil plant are very poisonous to people,
animals and insects; just one milligram of ricin (one of the main toxic proteins in the plant) can kill an adult.

Beans inside a Ricinus seepod

Anthuriums

The plant cells contain needle-like crystal of insoluble calcium oxalate
which penetrate the skin and mouth causing discomfort.
In addition, the plants contain proteolytic enzymes which release histamine and kinins,
causing swelling and an itching or burning sensation.