Possible Clues:

• Vocalizer's syllables
• Start of a common musical phrase
• Singer's space-filling syllables
• Typically refrain from extra-large portion
• Joyous refrain in song
• Syllables sometimes sung while skipping
• Part of a skipping refrain
• Tenor initially rehearses in the manner of a hum
• Start of a music refrain
• Part of a carefree song refrain