Do not bring an Easter lily (or any other lily) into your home or souside where cats could come in contact with them.
This is from the Pet Poison Hotline –
The most dangerous and potentially life-threatening lily ingestions by cats involve lilies belonging to the genera Lilium (true lilies) and Hemerocallis. Examples of some of these toxic lilies include Asiatic, Easter, Japanese Show, rubrum, stargazer, red, tiger, Western, and wood lilies (Lilium species) and daylilies (Hemerocallis species). Even small ingestions (such as less than 1-2 petals or leaves) – even the pollen or water from the vase – may result in severe, acute kidney failure.
If you suspect your cat has ingested any part of one of these lilies, bring your cat (and the plant) immediately to a veterinarian for medical care. DO NOT WAIT – Take to vet immediately.