It's all about melisma, volume, pitch and the duration of notes.
British Dictionary definitions for melisma
melisma
/mɪˈlɪzmə/
noun (pl) -mata (-mətə), -mas
1.
(music) an expressive vocal phrase or passage consisting of several notes sung to one syllable
Derived Forms
melismatic (ˌmɛlɪzˈmætɪk) adjective
Word Origin
C19: from Greek: melody
Word Origin and History for melisma
n.
1837, from Greek melisma "a song, an air, a tune, melody," from melos "music, song, melody; musical phrase or member," literally "limb," from PIE *mel- "a limb." Related: Melismatic.