miming adverts

[bonsaimaster]

why do some adverts that have celebs on have another voice that you no isnt theres mimed over their voice?

[jennyfluffy]

her name is Regina Spektor its called us. its a lovely song isnt it!
enjoy
Jenny x

[smoker1]

Jennyfluffy.Eh?!!!!!!!!!!!!!!!!!!!!!!

[Rufio]

You what love?? Keep taking them pills....
Anyway, some of them are because its a global company which shows the same advert in different countries and the original wasnt filmed in English. Not sure about the rest.