You've probably heard that poinsettias don't belong in homes with cats, and the plants could indeed cause some discomfort, although ASPCA says the toxicity threat is generally exaggerated. Another common plant is much more dangerous. "A household with a cat should never have a lily in it, ever," says Dr. DeClementi. Cats are attracted to the greenery, but munching on a lily-containing bouquet could lead to kidney failure. "Lilies are very poisonous," Dr. DeClementi warns.