‘A sharp tongue’ is merely a metaphor. It should be readily understood in and of itself, despite its impossibility. Even in the passage quoted, wouldn’t ‘a’ suit the metre better?
’The pointing finger’ seems proverbial and suggests an archetype; a one-of-a-kind meme, trope or cultural icon symbolic of an eternal truth and yes, a Platonic ideal.
Anciently Isaiah (58:9-12) invokes ‘If you take away the yoke from your midst, THE POINTING OF THE FINGER, and speaking wickedness… then you will call and the Lord will answer…’ in which a third article would surely describe ‘the speaking of wickedness…’
Clearly John the Baptist used ‘a’ and not ‘the’ finger to point Jesus out but only weeks ago, Pope Francis re-told that story choosing exclusively ‘the’ over ‘a’ for 11 nouns or adjectives that not only could have been indefinite, but would have made his point more clearly if they had been… as with ‘…the preacher of repentance and baptizer who points to the true baptizer in the Holy Spirit”. Of course ‘the true baptizer in the Holy Spirit’ merits definite articles but the distinction would be the greater if John were merely ‘a preacher’ or ‘a baptizer’
The Pope sees that as so important that ‘The vocation of all Christians is “to be witnesses to Jesus”, to fill their lives with the“gestures” typical of John the Baptist: “pointing to Jesus”.’
Glossing over the words on Belshazzar’s wall because that finger was writing, not pointing, Omar Khayyám also used ‘the’ not ‘a’ for his Moving finger, Agatha Christie kept that ‘the’ when she swiped the line for a book title.
Getting back to pointing, 1919-32 saw at least three films entitled ‘Pointing Finger’ films use ‘The.’
Is all this just pretentiousness, at which the finger of scorn should be pointed?