Why does Ayu move her mouth to vibrato?

[TOBEAYU]

I try to explain this... But I want to apologize because you know... english isn't my mother tongue.
So, move the mouth when she is doing vibratos is a little trick, a little help to make the sound. Sometimes, specially when your voice isn't in a good condition, you need a little help to make some sounds with your voice.
There are a lot of little helps for singers to do some sounds when your voice isn't good... or you have a cold and need to performance (like AYU sometimes) and well... that's the reason why AYU moves her mouth sometimes. With this help she doesn't force her vocal chords (strings? I don't know how to say that but I hope you understand) so much, and she can take care a little more of her voice and vocal chords...

Imagine sing everyday or every two days two hours... without a rest. Your voice suffer a lot and with the pass of the time it finally sounds like... ****. xD

Well... I don't know if I've been able to explain myself.... xD I'm terrible! xD