What this means for learners
Gadsup and Telefol share 10 sounds — roughly 37% of Telefol's inventory overlaps with Gadsup. Shared sounds are ones a speaker already knows from their native language and will generally produce and perceive accurately without explicit training.
The 17 sounds found only in Telefol represent the greatest pronunciation challenge for Gadsup 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, Gadsup has 9 sounds not used in Telefol. Native Telefol speakers learning Gadsup 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.