Why your Beagle is the only concern here
Since only your 10 kg Beagle ate the steamed collard greens, focus your attention entirely on them. The other dog faces no risk from this incident, as collard greens don't transmit any harmful elements between pets. What matters now is how much your Beagle consumed and how they're reacting to it.
Steamed collard greens without added oils, salt, or seasonings are generally safe for dogs in small quantities. For a dog of your Beagle's size, a few bites from your plate shouldn't cause problems beyond possibly some extra gas. Watch for any changes in their usual bathroom habits or appetite over the next day.
What to expect in the next 12 hours
Most dogs handle small amounts of plain vegetables without issue, but individual sensitivities vary. Your Beagle might show absolutely no reaction, or could experience mild digestive upset like slightly looser stools. This isn't an emergency, just their system adjusting to unfamiliar fiber.
The timeframe matters here - problems would appear within half a day if they're going to occur at all. If your dog remains their normal self after 12 hours with no vomiting, diarrhea, or loss of appetite, you can stop monitoring specifically for this incident.
When the other dog would need attention
Your uneaten collard greens pose no danger to the dog who didn't consume them. There's no toxin in collard greens that transfers between animals, and no risk of secondary poisoning from one dog to another in this case.
The only scenario where your other dog would need monitoring is if they start showing similar symptoms without having eaten the greens - that would indicate an unrelated illness. But since collard greens aren't the culprit here, you can rest easy about that possibility.
Making vegetable sharing safer in future
While this incident isn't cause for alarm, there are smarter ways to share human foods with pets. Always offer vegetables separately, in controlled amounts appropriate for each dog's size, rather than letting them snatch from plates.
Steaming makes greens easier to digest than raw, and skipping all seasoning is crucial. For multiple dogs, prevent competition by giving treats simultaneously in separate areas. That way you avoid situations where one pet gets everything and the other gets nothing.
The full verdict, portion guidance and serving notes are collected on the Collard greens food facts page.