Chocolate, cola drinks, tea and acai berries contain a substance that can be poisonous to dogs, said Rosemary LoGiudice, veterinarian at Furnetic, a Chicago veterinary clinic associated with the Chicago Center for Veterinary Medicine and the University of Illinois School of Veterinary Medicine.

"One other thing regarding chocolate toxicity in dogs, cocoa bean mulch, which is often used in landscaping, contains the same substance that is in chocolate, so if this mulch is eaten it can cause poisoning in dogs, too," LoGiudice said.

Theobromine is the name of the substance that can cause dogs to become very sick. Different kinds of chocolate contain different amounts of theobromine.

"In low doses, it can cause relatively mild problems such as intestinal upset or hyperactivity. In higher amounts it can cause the heart to beat irregularly and can cause a heart attack, seizures or even death. Because of their size, smaller dogs are more sensitive to theobromine than larger dogs," LoGiudice said.

In humans, theobromine sometimes is used in medicine to expand arteries, cause frequent urination or stimulate the heart.

Why would the same substance be harmful to dogs but possibly helpful to humans?

"The dose given medically to people is carefully measured. In addition, peoples' larger size would enable them to manage it better," LoGiudice said.

Keep pets away from food they're not supposed to eat.

"Dogs will figure out who is the weakest link and go to them for treats," LoGiudice said. "We see many of these cases around holidays when people tend to have lots of chocolate goodies around."

What if your dog eats chocolate or something else that makes him or her sick?

"Always call the veterinarian," LoGiudice said. The veterinarian can tell you if first aid items at home can help your pet, or if the pet would be better off under a doctor's care.

Just in case, keep a few first aid items at home.

"Hydrogen peroxide, used only as a veterinarian advises, bandage materials, first aid ointment like triple antibiotic cream, eyewash, antiseptic wash. Call the vet with any questions," LoGiudice said.