The daffodil (also known as narcissus, jonquil, or paper white) is the traditional harbinger of spring, right alongside tulips, which are also poisonous to cats. While they are beautiful, these pretty flowers (along with their stems, leaves, and bulbs) can cause vomiting, diarrhea, convulsions, low blood pressure, tremors, and cardiac arrhythmias if consumed by your cat.
When it comes to plants grown from bulbs, including daffodils and tulips, it is the bulb that is most toxic to pets. If you have these in your garden, you might need to take measures to discourage your cat from digging up the bulb.