A pet dog lying sulkily on the street jumps up at a single "Hello" from its owner. When the same phrase is repeated, it wags its tail or approaches to express friendliness. This is the so-called "Hello" test currently trending among pet owners on social networking services (SNS). While it might be assumed that dogs understand the meaning of human words or speech, experts generally agree that this is far from reality. They explain it as a kind of reflex action resulting from long-term learning associated with "good memories."

◇ Connecting auditory signals with repeatedly occurring events

Research findings consistently emerge from academia showing that dogs learn by connecting specific human sounds, intonations, gestures, and situations, and use this to predict intentions or subsequent actions. The aforementioned phrase "Hello" differs from the concept of a greeting found in a dictionary from a dog's perspective. Rather than having the abstract meaning of "inquiring after someone's well-being," it is analyzed as a conditioned response where a specific auditory signal is linked to a repeatedly occurring event that follows. 

For instance, if an owner says "Hello" in a bright voice and pets the dog every time they return home, the expression can become a signal to the dog that a welcome person is appearing or that attention and physical contact will follow. If the same phrase was repeated while preparing for a walk, the sound "Hello" itself could serve as a cue anticipating an outing. Ultimately, what a dog reacts to is closer to the correlation formed between sound, situation, behavior, and reward than the dictionary definition of a single word. There is a wide individual variance in how many words dogs can learn. Dogs that have undergone repetitive training are known to distinguish a significant number of words.

A representative case is Chaser, a Border Collie. Chaser was reported to have distinguished the names of over 1,000 toys through long-term training. Given that learning abilities vary greatly depending on the breed, amount of training, and interaction with the owner, this is far from the average of typical pet dogs. General pet dogs can also connect frequently encountered sounds—such as "walk," "treats," "food," "stay," and "sit"—with specific behaviors or objects through repetitive experience.

Crucially, the ability to distinguish words differs from the ability to understand sentences like a human does. Just because a dog reacts to the sound of "walk," it cannot be assumed that it understands the grammatical structure and future circumstances of a sentence like "Let's go for a walk in the park this evening" in the same way humans do. An official from the Korea Kennel Federation stated, "In the process of dogs accepting human speech, an element as important as the content of the voice is intonation, pitch, and intensity—so-called 'prosody.'

A dog's reaction can vary depending on the tone of voice used, even for the same word." They continued, "While a dog wags its tail or approaches when an owner praises it in a bright, high-pitched voice, it will show a different reaction if the same word is spoken in a low, threatening voice. In particular, dogs respond sensitively to the voices and tones of people familiar to them." This implies that a stranger saying "Hello" in a bright tone and a long-time owner saying the same word with their usual intonation can be entirely different signals to a dog. In other words, it is analyzed that dogs utilize not only "what sound was heard" but also "how it was spoken."

The reason pet dogs appear to understand their owners' words cannot be explained by auditory signals alone. They simultaneously observe the commander's facial expressions, gaze, gestures, posture, movements, and surroundings. If an owner walks toward the front door and picks up a leash while saying, "Shall we go for a walk?", the dog understands the series of actions combined with the word, rather than just the word itself. Because of this, owners may think their dogs understand their words precisely, but in reality, multiple signals may have been transmitted simultaneously. For example, if a dog runs over not just upon hearing the words "Let's eat," but after seeing the owner move toward the kitchen and pull out the food container, the dog is predicting upcoming events by combining language and action.

◇ An "interactive dialogue" can be formed

Can true communication with a dog be achieved then? Realistically, human-to-human levels of verbal conversation are difficult. Of course, that does not mean communication itself is impossible. Dogs regulate their behavior through human words, intonations, and gestures, and conversely convey their state or demands through barking, whining, gaze, posture, and tail movements. Owners also learn what a dog's behavior means by repeatedly observing these signals. In this regard, a sort of "interactive dialogue" can be formed between humans and dogs. 

While it is not a conversation consisting solely of human language, a communication system is created where they exchange signals and regulate behavior. Recently, augmented and alternative communication (AAC) methods—where pet dogs press multiple buttons to express words like "walk," "food," "play," and "mom"—have also been drawing attention. An official from an animal rights organization explained, "It is actually observed that some dogs use buttons by associating them with specific objects or actions," adding, "stricter experiments and long-term observation are required to distinguish whether dogs have learned the meanings of buttons stably or if it is due to accidental behavior or owner inducement."

They emphasized, "It is necessary to be cautious about concluding that dogs understand sentences or express their thoughts in human language based solely on videos uploaded to social media. Ultimately, experience is more important than 'words.'" They added, "Dogs distinguish the meanings of words, intonations, and gestures accumulated through numerous experiences and use those combinations to predict people's subsequent actions. In that respect, there is a more sophisticated communication between dogs and humans than we might think."

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