Most baits we use to control rodents are anticoagulant. They have a chronic effect to prevent the target species becoming bait shy. This means that they have to feed on the bait for 4 or more days before it becomes lethal to the animal.
Often when an animal is poisoned they will die in their sleep so will die in the nest, trying to sleep of the effects of the poison. Sometimes however they will try and get one last meal to fend off the poison without realising that the trusted food source is the poison.
This mouse was found in such a manner on a bait tray that was positioned under a kitchen plinth.