What this means for learners
Epena and Yao share 20 sounds — roughly 41% of Yao's inventory overlaps with Epena. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 29 sounds found only in Yao represent the greatest pronunciation challenge for Epena speakers. The adult brain tends to map unfamiliar sounds onto the closest native equivalent — a process that produces the characteristic "accent" of a second-language speaker. Learning to hear and produce these sounds as distinct requires focused ear training, not just repetition.
Conversely, Epena has 18 sounds not used in Yao. Native Yao speakers learning Epena will face the mirror-image challenge with these sounds.
Phoneme inventories from PHOIBLE. Data reflects one documented inventory per language; some variation exists across dialects and sources.