Plums (pitted) — Food safety facts
Feed with care · Dogs · full breakdown on the linked food page
Flesh in small pieces is fine. The pit is a choking and cyanide risk.
Short answer
A few pieces of plum flesh without the pit are only a mild risk for your dog. The fruit flesh is fine in small, bite‑size pieces. Keep an eye for vomiting, diarrhea, or any sign of choking. If any of those appear, call your vet.