May be caused by spoiled food, poisoned meat set out to destroy pests, mice killed by arsenic, household or garden chemicals, or poisons cruelly fed to the animal by others. Other household poisons are lead, petroleum distillates, detergents, lye, cleansers, mothballs and medications such as aspirin. It is almost never possible to notice poisoning at the moment it occurs.

SOURCE: cat.consultinghealth.com