Which of the following is a severe clinical sign associated with bufo toxin ingestion?

Cyanosis is considered a severe clinical sign associated with bufo toxin ingestion. This condition results from a lack of oxygen in the blood, leading to a bluish discoloration of the skin and mucous membranes. When an animal ingests bufo toxins, which are secreted by certain toads (for example, the Colorado River toad), they can experience severe cardiovascular and respiratory distress. The bufo toxins can cause significant toxicity, leading to decreased oxygenation of the blood, which manifests as cyanosis.

In contrast, while hypersalivation, pawing at the mouth, and retching can also be signs of bufo toxin ingestion, they are typically considered less severe compared to cyanosis. Hypersalivation and pawing at the mouth may indicate discomfort or irritation in the oral cavity but do not necessarily indicate a life-threatening condition. Retching, which is more related to gastrointestinal distress, is also less of an acute threat compared to cyanosis. Thus, the presence of cyanosis indicates a more critical and potentially life-threatening situation that requires immediate veterinary attention.