Though aloe vera is great for us humans for skin-soothing purposes, it is highly toxic to dogs and cats. The gel inside the leaves doesn't do any damage, but the ingestion of the leaves can have multiple dangerous effects on dogs, such as diarrhea, vomiting, depression, tremors, and anorexia.

Another beautiful flower, the popular holiday ornamental, and toxic amaryllis can cause a variety of problems when consumed by both dogs and cats, from vomiting, diarrhea, abdominal pain, and hypersalivation, to anorexia, depression, and tremors. Like daffodils, the bulbs contain the most highly concentrated toxins.

Azaleas are considered one of the most poisonous plants to pets, as all parts of the plant are classified as moderately to extremely toxic. Grayanotoxin, the toxic principle of the plant, affects the functioning of the muscles and heart. Even a small amount consumed, such as the ingestion of just a few leaves, can lead to drooling, vomiting, diarrhea, low blood pressure, paralysis, depression, and/or cardiac failure.

Summertime lets you grow some of the prettiest flowers, but unfortunately, many of these plants are considered poisonous to your pets, including daffodils. Although the entire plant is considered poisonous to pets, the most danger lies in the very toxic bulb. Consumption can have side effects of vomiting, hypersalivation, tremors, low blood pressure, diarrhea, convulsions, and cardiac arrhythmias. The toxic principle of alkaloids in the flower is most highly concentrated in the bulb, so if your pet loves to dig up your garden you may want to reconsider planting daffodils.

Hydrangeas are garden stunners, but, like daffodils, these pretty flowers can cause a great deal of harm to your cat or dog. Symptoms of hydrangea consumption can range from hypersalivation and other oral irritation to vomiting, diarrhea, and depression.

Though it's improbable that your pets will decide to make a meal out of a wall of ivy, it's smart to know the dangers of it if you have some at your home. Digestion of any common ivy leaf in dogs can lead to vomiting, diarrhea, abdominal pain, hypersalivation, and oral irritation. More extreme symptoms can even be as serious as paralysis and comatosis, so be sure to keep ivy out of reach from pets or monitor them if they go near the plant.

Highly poisonous both to humans and pets, oleanders are a popular flower whose leaves contain cardiac glycosides, a toxin that can cause diarrhea, abdominal pain, depression, colic, trouble breathing, tremors, and possible cardiac failure when ingested.

Ripe tomatoes are generally safe to eat for dogs, but consumption of parts of the tomato plant and young, green tomatoes are a different story. Tomato plants aren't lethal (unless your pet has ingested a very high amount of the plant) but it does contain poisonous toxins that can cause great discomfort in dogs and cats, such as severe abdominal pain, diarrhea, vomiting, hypersalivation, depression, slow heart rate, weakness, and paralysis.