The initial idea of Black Box can be traced to two-port networks (quadripoles) that were created by a German mathematician, Franz Breisig, in 1921. A Black Box is a system or object which is purely external or phenomenological and its internal constitution and structure is unknown or irrelevant to being opened for inspection. When TCVM diagnosis was developed several thousand years ago, ancient healers did not have modern diagnostic tools such as laboratory tests, radiography, ultrasound, scintigraphy and magnetic resonance imaging (MRI). Instead, the ancient medical practitioners could only rely on their senses to gather information about a patient’s condition. “To know the inside by examining the outside” is the fundamental principle of Traditional Chinese Veterinary Medicine (TCVM) diagnostics. Thus, the animal body is treated as a Black Box. The TCVM approach is like the Black Box. External information (clinical signs) displayed by patients is used to diagnose the correct TCVM Pattern which enables the veterinarian to select an appropriate treatment correctly matched to the pattern. A discussion of this very useful approach, especially in clinical cases when a Western diagnosis is not available or is unable to pinpoint the etiology of a disease is presented.