European crab apple poses a mild toxicity risk to humans, primarily through ingestion of seeds, leaves, and stems, containing hydrogen cyanide. Symptoms include dizziness and headaches. European crab apple is moderately toxic to cats causing shock if large amounts are consumed. In dogs, leaves, twigs, and seeds cause reactions like vomiting and diarrhea, with death being rare. Avoid accidental ingestion, especially by pets and children.