Your pet's digestive enzymes are not the same as your digestive enzymes.
Our bodies DO have the digestive enzyme necessary to digest onions. The digestive systems of some animals, such as dogs, cats and guinea pigs, do NOT have the enzyme necessary to digest onions.
All onions, raw or cooked, are a danger – a poison – to these pets.
We will spare you the details here, but even small amounts of onions cause serious distress to their systems. YOU may or may not notice, depending on the amount ingested and the degree of interaction you have with your pet.
Not noticing is one matter. Causing it is another.
In a land far away, there is a homemaker who often serves raw, thinly sliced onions. During meals, each family member is free to select what amount he or she wants… in a lettuce or cabbage wrap sandwich, added to black beans, or whatever the meal. At times there are leftover onion slices. Does she place them in the refrigerator to be used the next day? Does she enclose them in a plastic container with a tight lid? Does she enclose them in a glass container with a lid? What does she do with those leftover onion slices? She sets them in a glass bowl and positions that as a kitchen table centerpiece, where it generally remains until the next morning.