In this comparative cross-linguistic study we test whether expressive interjections (words like ouch or yay) share similar vowel signatures across the world's languages, and whether these can be traced back to nonlinguistic vocalizations (like screams and cries) expressing the same emotions of pain, disgust, and joy. We analyze vowels in interjections from dictionaries of 131 languages (over 600 tokens) and compare these with nearly 500 vowels based on formant frequency measures from voice recordings of volitional nonlinguistic vocalizations. We show that across the globe, pain interjections feature a-like vowels and wide falling diphthongs ("ai" as in Ayyy! "aw" as in Ouch!), whereas disgust and joy interjections do not show robust vowel regularities that extend geographically. In nonlinguistic vocalizations, all emotions yield distinct vowel signatures: pain prompts open vowels such as [a], disgust schwa-like central vowels, and joy front vowels such as [i]. Our results show that pain is the only affective experience tested with a clear, robust vowel signature that is preserved between nonlinguistic vocalizations and interjections across languages. These results offer empirical evidence for iconicity in some expressive interjections. We consider potential mechanisms and origins, from evolutionary pressures and sound symbolism to colexification, proposing testable hypotheses for future research.