Every October the ground under an oak tree turns into a carpet of small brown missiles, and every October some dog decides they are snacks. The ones who crunch them are why this is worth two minutes of your week.
Acorns are not poisonous in the dramatic sense. The problem is duller. They carry tannins, the bitter compounds that make a raw acorn taste awful to you and apparently fascinating to a Labrador. A few will upset the gut; a steady diet can damage the kidneys and liver, the same reason oak toxicosis is a known problem in livestock. Farmers’ Almanac has a good rundown.
Then there is the shape. An acorn is hard, round, and about throat-sized for a small dog. For a big dog one may pass through without drama. For a terrier it is a marble in a garden hose. The AKC flags choking and blockage as real outcomes.
What you would see: vomiting that will not settle, diarrhea, a dog who turns down dinner, a belly sore to touch, or a pup who cannot get comfortable. Vomiting that repeats after you watched them swallow something is a call to the vet, not a wait-and-see.
Do not try to make your dog vomit at home. Cornell’s veterinary school and the AKC both warn against it, because whether it helps depends on what went down and how big the dog is. Let the clinic decide.
You do not need to rake the entire yard. Clear the spots your dog actually uses: the run, the patio, the potty corner. Keep the leash short under a heavy-producing oak. Drill “leave it” now, while the reward for listening is avoiding a mouthful of tannins. Same skill that keeps them off the wild mushrooms popping up this month.