Which of the following is a non-linguistic cue?

Facial expressions serve as non-linguistic cues because they convey emotions, attitudes, and additional context without the use of language. When communicating, people often rely on facial expressions to enhance or modify the message being conveyed verbally. These visual signals can indicate feelings such as happiness, sadness, confusion, or frustration. Unlike linguistic cues, which involve words and grammar, facial expressions are universally recognized across cultures and are not dependent on language proficiency.

In contrast, vocabulary usage, grammar, and phonetics all pertain to linguistic elements of communication. Vocabulary refers to the words we use, grammar involves the rules that govern sentence structure, and phonetics pertains to the sounds of speech. Each of these is essential in forming coherent and understandable language, but they do not fit the definition of non-linguistic cues. Thus, facial expressions distinctly embody the essence of a non-linguistic cue by providing meaning and context without relying on interaction through language.