What happens when a dog eats laundry powder?
Take it to the vet for emergency treatment. Grab the laundry powder as well, so the veterinarian can read the ingredient label and provide treatment accordingly. If you get to the vets fast enough, they will be able to evacuate your dog's stomach, hopefully before any real damage has been done. If you take a 'wait and see' approach, by the time symptoms show, it will be too late and treatment will be long and expensive.
Laundry powder tends to be pH basic, so you may see signs of caustic burns in the mouth or upper gastrointestinal tract - excessive salivation, vomiting, painful red erosion in the mouth and on the tongue, refusal to eat, etc. Severe signs of problems would include depression, lethargy, pale gums and a bloating stomach - these could be related to a bleeding ulcer in the stomach that can be life-threatening.