What this means for learners
Ao-Naga and Garo share 17 sounds — roughly 49% of Garo's inventory overlaps with Ao-Naga. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 9 sounds found only in Garo represent the greatest pronunciation challenge for Ao-Naga 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, Ao-Naga has 18 sounds not used in Garo. Native Garo speakers learning Ao-Naga 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.