The gleam-glum effect is a novel sound symbolic finding that words with the /i:/-phoneme (like gleam) are perceived more positive emotionally than matched words with the /Λ/-phoneme (like glum). We provide data that not only confirm the effect but also are consistent with an explanation that /i:/ and /Λ/ articulation tend to co-occur with activation of positive versus negative emotional facial musculature respectively. Three studies eliminate selection bias by including all applicable English words from the English Lexicon Project (Balota et al., 2007) and the Warriner et al. (2013) database and every possible Mandarin Pinyin combination that differ only in the middle phoneme (/i:/ vs /Λ/). In Study 1, 61 U.S. undergraduates rated monosyllabic English /i:/ words as robustly more positive than matched /Λ/ words. Study 2 analyzed the Warriner et al. (2013) valence ratings, extending the gleam-glum effect to all applicable words in the database. In Study 3, 38 U.S. participants (using English) and 37 participants in China (using Mandarin Pinyin) rated word pairs under three conditions that moderate musculature activity: Read aloud (Enhance), read silently (Control), and read silently while chewing gum (Interfere). Indeed, the effect was both replicated and was significantly larger when facial musculature was enhanced than when interfered with, and the two language populations did not significantly differ. These findings confirm a robust gleam-glum effect, despite semantic noise, in English and Mandarin Pinyin. Furthermore, these data are consistent with the hypothesis that this type of sound symbolism arises from the overlap in muscles used both in articulation and emotion expression. (PsycInfo Database Record (c) 2021 APA, all rights reserved).