It would be extremely rare (*unheard of) for your pet to pass away from ingestion of onion the night before. The chemical reaction of thiosulphate on red blood cells would take several days to manifest.
How Much Onion Kills A Dog?
Onions are harmful to dogs. It damages red blood cells and is the main reason for anemia in dogs. Severe condition can cause any thing like death. For more information about the food harmful for dogs, visit the link below.
Food harmful for dogs
Food harmful for dogs
No
Not surprisingly, pets actually have to eat the onions to get sick, but depending on their size, they may not have to eat much. One fourth of a cup can make a 20-pound dog sick while several cups may be needed to make a large dog sick.
A small dog can become ill and die on a much smaller amount of onion than a larger dog. But the safe thing is to give NO onion as it is lethal to dogs.
I think it's ridiculous that the right to bear onions is under attack again. Onions don't kill dogs. People with onions kill dogs!
Onion and Garlic are not good for dogs as they both contain toxic ingredient thiosulphate. Because of this the dog can get haemolytic anaemia. You can say that onion can kill a dog. For more information, visit the following website.
Onion and Dogs
Onion and Dogs