Which lines in this excerpt from Book 12 of Homer's Odyssey reveal that the monster Scylla cannot be defeated in battle, even by a great warrior such as Ulysses?
Ah, shun the horrid gulf! by Scylla fly.
'Tis better six to lose, than all to die.'

"I then: 'O nymph propitious to my prayer,
Goddess divine, my guardian power, declare,
Is the foul fiend from human vengeance freed?
Or, if I rise in arms, can Scylla bleed?'

"Then she: 'O worn by toils, O broke in fight,
Still are new toils and war thy dire delight?
Will martial flames for ever fire thy mind,
And never, never be to Heaven resign'd?
How vain thy efforts to avenge the wrong!
Deathless the pest! impenetrably strong!
Furious and fell, tremendous to behold!
E'en with a look she withers all the bold!
She mocks the weak attempts of human might;
Oh, fly her rage! thy conquest is thy flight.
If but to seize thy arms thou make delay,