Christina Aguilera Live David Letterman Walk Away

Im a huge fan of xtina!! i was just noticing that she forgets the lyrics of her songs...in a presentation on MTV she forgot a part in "Oh Mother" and in this performance she did as well in the part where she says: Every time i try to breath for air, im smothered in dispair is never over over oh oh..oh, and then she should have said: seem i'll never wake from this nightmare etc....and just said something else haha!! but it was cool she didnt make it obvious!!!