Mouse poison doesn't kill the mouse instantly so you may notice the mouse coming back into your house after more poison after you set some more out.
Mouse poison can take between 1 to 5 days to kill the mouse or mice after they eat the poison so if you notice the mouse or mice coming back after eating the poison the mouse will likely die a few days later.
If the weather is warm enough then you might smell a decomposing mouse or mice under your house or in your walls etc.
The mouse poison works by preventing the mouses blood from clotting and then causes internal bleeding which is what slowly kills the mouse.
So it's a slow death and not instant death for a mouse.