What this means for learners
Yay and Yao share 27 sounds — roughly 55% of Yao's inventory overlaps with Yay. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 22 sounds found only in Yao represent the greatest pronunciation challenge for Yay 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, Yay has 11 sounds not used in Yao. Native Yao speakers learning Yay 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.