This pronunciation change is about ‘ㅎ’. In Korean, there are lots of changes with this letter ‘ㅎ’. When ‘ㅎ’ meets ‘ㅅ’, the pronunciation changes to ‘ㅆ’. And when ‘ㅎ’ meets ‘ㄱ,ㄷ,ㅂ,ㅈ’, the pronunciations change to ‘ㅋ,ㅌ,ㅍ,ㅊ’ .
1. ㅎ(final consonant) + ㅅ => ㅆ
2. ㅎ(final consonant) + ㄱ,ㄷ,ㅂ,ㅈ => ㅋ,ㅌ,ㅍ,ㅊ
3. ㄱ,ㄷ,ㅂ,ㅈ(final consonant) + ㅎ =>ㅋ,ㅌ,ㅍ,ㅊ
e.g)
You can listen to the pronunciation here.
Funkorean4u.com 