Rodent bait used to exterminate mice and rats can also be deadly to dogs and cats. If you have pets then rodenticides should be used with extreme caution.
There are many types of rodent baits or traps on the market, most kill rodents with anticoagulants. Anticoagulants cause internal bleeding, the rodents bleed to death. If a dog or cat ingests the rodenticide then the poison will have the same effect on its body, without treatment the dog or cat will bleed to death.
If you must use rodent baits or rodenticides be sure to place the pellets in places that dogs and cats can not get to. Consider using humane traps instead, they will help keep family pets out of danger.