I asked AI.
Google Gemini Answer
Here’s what you should do about your cat eating a mulberry in the US:
Relax, ripe mulberries are not poisonous to cats. A small amount likely won’t cause any problems.
Monitor your cat. Look for signs of digestive upset like vomiting, diarrhea, or loss of appetite. If you see any of these signs, or if your cat seems lethargic, then contact your veterinarian.
Be aware of the risks of unripe mulberries and mulberry parts. The unripe fruit, leaves, and stems of a mulberry tree contain a white sap that can be irritating to the skin and stomach. This sap can also have hallucinogenic effects. If you think your cat might have ingested something other than the ripe fruit, call your vet.
Generally, a cat’s digestive system isn’t suited for fruits. While a single mulberry probably won’t cause harm, avoid letting your cat eat them regularly.
If you’re concerned about your cat ingesting mulberries or other potentially harmful plants, consider keeping them out of reach or fencing off the area around the tree.