ZZ plant (Zamioculcas zamiifolia) is mildly toxic — calcium oxalate crystals cause stomach upset.
Reputation as 'deadly toxic' is exaggerated, but ingestion is still unpleasant.
ZZ plants contain insoluble calcium oxalate crystals throughout the leaves, stems and rhizome. They cause oral irritation, drooling and vomiting. The sap can also irritate skin.
Fonti
Most cases need only supportive care. Wash hands and rinse the dog's mouth after exposure.