Complex sentence: Additionally, the mouth radical (口, "kǒu", to indicate a character used for its sound only) is often used in character compounds for the transliteration of heterocyclic names, (e.g., 吡啶, "bǐdìng", pyridine).
Split into simpler sentences: Additionally, the mouth radical (口, "kǒu") is affixed to characters that are used for their sound only. This occurs often in the transliteration of the names of heterocyclic compounds, (e.g., 吡啶, "bǐdìng", pyridine).