Spring bulbs (tulips, hyacinths) are toxic to cats and dogs.

As spring approaches, don’t forget about the dangers of spring bulbs to your dog! Both hyacinths and tulips belong to the Liliaceae family, and contain allergenic lactones or similar alkaloids. The toxic principle of these plants is very concentrated in the bulbs (versus the leaf or flower), and when ingested in large amounts, can result in severe clinical signs. Severe poisoning from hyacinth or tulip poisoning is often seen when dogs dig up freshly planted bulbs or having access to a large bag of them. When the plant parts or bulbs are chewed or ingested, it can result in tissue irritation to the mouth and esophagus. Typical signs include profuse drooling, vomiting, or even diarrhea, depending on the amount consumed. With large ingestions, more severe symptoms such as an increase in heart rate, changes in respiration, and difficulty breathing may be seen.

http://www.petpoisonhelpline.com/poison/tulip/

Thanks to Pet Poison Helpline for this information!