English-speaking movies and television series are flourishing in Hong Kong, and Chinese screen subtitles are often provided to the audience. Studies relating to subtitling have often discussed reduction methods and reduction categories, but little work has touched on the areas of and reasons for under-translation. The author has observed that sexually suggestive information is often under-translated in English-Chinese subtitling. Some instances suggest that the under-translation is related to the translator’s ignorance of English idiomatic usage, or the translator’s insensitivity of the translation to the implicit information. Some other example indicates, however, that the translator is neither ignorant nor insensitive about the implied meaning. The translator has shown in the subtitling that he or she knows the implicit meaning, and that attempts were made to tone down the message a great deal, probably out of socio-psychological, cultural and euphemistic reasons. These observations based on video-taped examples have identified the existence of non-linguistic constraints in cross-linguistic and cross-cultural activities such as translation.