I’d never heard that about cherries and grapes. I worked at an animal hospital and learned that the amount of chocolate and size of the dog had to be considered, so if a chocolate chip or even a Hershey’s Kiss hits the ground, the dog can enjoy an unintended treat.
Years ago in Kentucky horse country, a horse farm were losing foles to miscarriage and still birth. An autopsy revealed arsenic poisoning. Immediately there was an investigation of everyone and anyone that had been on that farm. They thought someone was poisoning the mares. During the investigation some of the mares were in a particular pasture with some wooded area. The mares were going into the wooded area and eating unripe and ripend cherrys. It seems this pasture had wild cherry trees growing and the mares would go in it for the cherrys. Cherrys contain a small amount of arsenic, eat a lot of cherrys and you can get a lot of arsenic, eat pounds and pounds of cherrys and you get a lot of arsenic. That’s where the mares were getting the arsenic and effecting the unborn foles. They burned down the whole wooded area and every other cherry tree on the farm. No more stillborn foles.