They interfer with the activation of several factors in the clotting system and the poisoned animal can bleed to death. Good information on anticoagulant rodenticide intoxication is available at the Cornell University Veterinary School site. The other type of rat and mouse poisons that cause toxicities in dogs and cats are vitamin D rodenticides. Large quantities of vitamin D cause massive increases in the blood calcium and kidney failure. A number of outdoor plants and house plants are toxic to animals.
Many plants are just gastrointestinal irritants and cause vomiting.
Others are far more dangerous. One example is the Easter Lily, which can cause severe and often fatal kidney failure. The following internet sites have information on poisonous plants. Some drugs that humans use routinely are highly toxic in pets. The drug damages feline hemoglobin rendering it incapable of carrying oxygen.