What this means for learners
FASU and Yao share 12 sounds — roughly 24% of Yao's inventory overlaps with FASU. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 37 sounds found only in Yao represent the greatest pronunciation challenge for FASU 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, FASU has 9 sounds not used in Yao. Native Yao speakers learning FASU 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.