Cat owners should avoid clumping clay litter at all costs. Not only is clay strip-mined (bad for the planet), but the clay sediment is also permeated with carcinogenic silica dust that can coat little kitty lungs (bad for the cat).

Plus, the sodium bentonite that acts as the clumping agent can poison your cat through chronic ingestion through their fastidious need to groom. Because sodium bentonite acts like expanding cement-it's also used as a grouting, sealing, and plugging material-it can swell up to 15 to18 times their dry size and clog up your cat's insides.Eco-friendly alternatives-popular brands include Feline Pine, Swheat Scoop, and World's Best Cat Litter-avoid these problems, because they contain no clay, silica, odor-absorbing crystals, or any synthetic additives that could upset kitty's gastrointestinal and immune systems. (Tip: Our favorite kitchen helper, baking soda, as well as dried, used green tea leaves, can help with that not-so-fresh smell.)

Flushable litters, however, remain controversial because cat doodie can contain Toxoplasma gondii, a parasite that enters felines after they've eaten infected rodents, birds, or other small animals. Although the cats later expel the parasites in their feces, the little buggers can survive in soil for more than a year, as well as foul up our drinking water.

Because most municipal sewage-treatment systems do not filter out Toxoplasma, the parasites can get flushed into ocean waters close to shore, and concentrate in mussels, crabs, and other filter feeders that sea otters nosh on. Hundreds of sea otters have been found dead off the coast of California in recent years, and some scientists believe that cat feces from flushable litter may be one of the culprits. Just another reason to keep your cat indoors.

Difficulty level: Easy