PHOENIX -- CBS 5 discovered five household items that can be dangerous for pets.

The first: macadamia nuts. The nuts contain an unknown toxin that can upset a dog's muscles and digestive tract.

The second: onions and garlic. They contain sulfur compounds that can cause gastrointestinal irritation and harm a pet's red blood cells.

A third problem is pennies. Not only can a furry friend choke on them -- pennies can do serious damage to the pet's digestive system.

Number four: lilies and other exotic flowers. Ingesting even a small amount can be lethal to a cat.

Number five: grapes and raisins. They can lead to vomiting and diarrhea in dogs.

Phoenix veterinarian Irwin Ingram said one of the problems is that the symptoms of toxic poisoning don't always show up right away, which means by the time the pet is brought in, it may be too late.

"When they don't start vomiting and get diarrhea, they show kidney failure over a period of time, and that's harder to diagnose," Ingram said.

For a list of other items that can be harmful to pets, click here.