My cat snatched and ate a couple of small bites of the flesh from a plum I was eating, is that dangerous?

A couple of small bites of plain plum flesh is usually not dangerous, but you should watch your cat closely. The main risks with plums are the pit, which contains cyanide and is a choking hazard, and the high sugar content which can upset some cats' stomachs. Since your cat only had the flesh, the immediate risk is low, but monitor for any vomiting, diarrhoea, or loss of appetite over the next 12-24 hours. If you notice any of these signs, or if you suspect the pit was also ingested, contact your veterinarian for advice.