Once a rat consumes the rat poison it can take up to 3 days for the rat to actually die from the rat poison.
So you may notice the same rat come back within a day or so and it might want to eat some more rat poison.
The way that rat poison works is the rat poison thins the blood of the rat and then causes internal bleeding of the rat.
The rat poison also prevents the blood in the rat from clotting so the rat eventually dies within 3 days of internal bleeding that cannot be stopped.
Rat poison does not kill rats instantly but instead it's a slow 3 days to death for the rat.
But as long as the rat consumes the rat poison they will eventually die within 3 days of eating the rat poison.