Rats and mice get lumped together as rodents, but almost everything about how you handle them differs: entry size, bait response, trap placement, and where the nest will be.
Telling them apart from the droppings
Mouse droppings are small, roughly rice-grain sized, and pointed at both ends. You find a lot of them, scattered widely, because mice deposit constantly as they travel.
Rat droppings are noticeably larger, capsule shaped, and found in smaller concentrated groups. Roof rat droppings are more pointed; Norway rat droppings are blunter.
Entry size and where they get in
A mouse needs about a quarter of an inch, a rat about half. Mice therefore get in almost anywhere, including gaps around pipe penetrations and under door sweeps.
Norway rats are ground-oriented: burrows, sewers, crawl spaces, basements, the bottom third of a building. Roof rats are climbers: soffits, attics, palm trees, power lines, the top third.
That difference decides where the inspection focuses. Searching an attic for Norway rats generally wastes a morning.
Behaviour that changes the treatment
Mice are curious and investigate new objects quickly, so traps placed well produce results within days.
Rats are neophobic. A new trap in a familiar run is avoided, sometimes for over a week. Traps are often set unset at first so the rats accept them before they are armed. Impatience is the most common reason rat trapping fails.
Why we avoid interior poison
A poisoned rodent dies wherever it happens to be, which is frequently inside a wall cavity. That converts a rodent problem into a dead animal and fly problem with no access point.
There is also secondary risk to pets, owls and other predators. Trapping plus exclusion is slower to describe but cleaner in practice.
What ends it permanently
Sealing. A building that cannot be entered does not need an ongoing trapping programme. Everything else is maintenance of a problem rather than a solution to it.