My dog ate rat poison.
Bring the box.
There is no single "rat poison": four different toxins are sold in near-identical pellets and blocks, and they need different, sometimes opposite, treatments. The package (or a photo of it) is the single most useful thing you can bring.
Published guidance is unanimous: identify the active ingredient before anything else, because treatment for one class can be useless or harmful for another. Find the box, bag, or bait station label and read the active ingredient and EPA registration number to the poison-control vet. If the package is gone, note the color and shape of the bait and where it came from. Then follow their direction: for several of these toxins the treatable window closes before the first symptom appears.
Pet Poison Helpline · 855-764-7661 ASPCA Poison Control · 888-426-4435The four kinds, in one breath
Anticoagulants (brodifacoum, bromadiolone, warfarin): block clotting; bleeding starts 3-5 days later; a vitamin-K antidote exists and works well started early. Bromethalin: brain swelling, no antidote, decontamination in the first hours is everything. Cholecalciferol (vitamin D3): tiny amounts cause kidney failure; expensive, week-long treatment; increasingly common since anticoagulant restrictions. Zinc phosphide (gopher/mole baits): releases toxic gas in the stomach; vomiting should only be induced outdoors or with windows down, the gas can sicken people too.
Why "he seems fine" is the trap
Every one of these poisons has a silent window: anticoagulants take days to empty the body's clotting factors, bromethalin's brain swelling builds over hours to days, and cholecalciferol's calcium rise takes 12-36 hours. Treatment started inside the silent window is dramatically more effective, and for bromethalin it is the only effective window.
What NOT to do
Do not wait for symptoms. Do not induce vomiting without professional direction (wrong for some classes, dangerous indoors for zinc phosphide). Do not assume "one pellet is nothing": cholecalciferol baits are dangerous in single-digit gram amounts for small dogs. Do not throw away the package.