It typically occurs when a predator eats an animal, such as a mouse, rat, or insect, that has previously been poisoned by a commercial pesticide.
If the level of toxicity in the prey animal is sufficiently high, it will harm the predator.
Mammals susceptible to secondary poisoning include humans, pets such as cats and dogs, as well as wild birds.
[not verified in body] Various pesticides such as rodenticides may cause secondary poisoning.
[1] Some pesticides require multiple feedings spanning several days; this increases the time a target organism continues to move after ingestion, raising the risk of secondary poisoning of a predator.