Rat poison ingestion will not cause any immediate illness. It takes 2-3 days to stop the blood’s clotting ability, and they then begin bleeding internally, which will cause death if left untreated. If you see them eating the bait, inducing vomiting can sometimes remove the poison before it is absorbed. Otherwise, a blood test after 2 days will show if the blood is clotting or not and treatment can be begun. The length of time they need treatment varies with the brand of bait, so it is important to know this for the vet’s information.