My brother had his two dogs die on him right in his backyard a couple days ago. The dogs ate something in the yard and within 3 hours when into seizures and died. The same yard that both of them ran around for hour and hours on end. Day after day.

We live in Pennsylvania. Does anybody know what kind of natural poisons (like bushes, mushrooms, etc) that are common in Pennsylvania that would kill a dog within 3 hours??? We still haven't ruled out somebody intentionally poisoning these dogs so need to know if there is anything natural that could do this? We know for sure that it wasn't any careless chemicals or anything like that that did this.

Thanks in advance!