Many people get a cat to keep rodents away. While this is a perfect job for a cat, be careful about keeping a cat around when you might also be using rat poison as well.
If a cat should ingest a poisoned rat, it will likely get sick as well. The lesson is clear. Poison and traps have no place if you have a cat to hunt down rodents. Cats are better rodent killers anyway so let your cat do its job and keep it safe by keeping poisons and traps away from the cat.