I've been sort of methodically going through some of the possibilities that may have led to Zelda's death. It's been a way of coming to terms with it for me. I like answers, you know?
So I've looked at things like commercial pesticides used in hotels (we had stayed at a hotel with her the night before) and various medications that we humans take that could have possibly fallen somewhere where she could have gotten a pill. It hasn't been fruitful.
Then I turned to plants. She had been nosing around in a flower bed that day. In that flower bed, I learned, were some hellebore plants. This is the first thing on my list that is not just possible but actually might be considered probable. The timeline fits (onset between 30 minutes and four hours). The amount needed to kill a dog is very small. It causes cardiac death. (Actually it has SEVERAL mechanisms, but cardiac mechanism is one of them.)
We are going to talk to the vet that did the necropsy about this possibility. I feel like we might never know if that was "it", but since she was IN that flower bed and the symptoms and timeline fit exactly, the theory is strong enough to actually consider it probable.
Hellebore is a nasty little plant, I've since learned. Pretty flowers, nasty history. It's also called Christmas rose and Lenten rose.
Keep an eye on your little goofballs.