The thing I thought about doing it was it's Comic Relief and you've got to be funny. So although I did try to sing properly it obviously has hilarious results when you can't sing.
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It used to be that you had to make female TV characters perfect so no one would be offended by your 'portrayal' of women. Even when I started out on 'The Office' eight years ago we could write our male characters funny and flawed but not the women. And now thankfully it's completely different.