My hamster ate 1/4 of a hydrangea petal, what should I do?

Hydrangea is toxic to hamsters; the whole plant is poisonous, more so the stems and leaves, and eating it causes colic, abdominal pain, diarrhea, vomiting, rapid breathing, blood in stool, weakness, and sweating.

So if a hamster eats a petal, take it to the vet promptly for induced vomiting and gastric lavage, and watch closely for those poisoning signs, which can be life-threatening. To avoid this, do not grow hydrangea at home.