After washing and rinsing, you ran wet fingers through wet locks and if it squeaked you knew it was clean.
It could not pretend to be clean. It could not hide in a multiple of theories about cleanliness. It could not proclaim on the basis of some formula that it was clean. It could not fool you by a philosophical straw man that it was clean.
It had to squeak.
If it didn't squeak it wasn't clean. If it did, you described it as 'squeaky clean.'
I don't know whether anyone else could hear your hair squeak or whether it was a conversation your hair had with you alone. It didn't matter. To you it was an infallible rule of cleanliness. Dried and combed, if it squeaked after washing, you knew your hair would shine.
I can transfer the same infallible rule to my own thoughts and words. If I have been speaking with someone or if I have been asked to give an opinion on a Bible story, I sometimes ask myself afterwards 'did my words squeak?'
They make us feel clean through the words they use and the squeak becomes our own because we take their thoughts on board.
They echo the words of Jesus, "You are already clean because of the words I have spoken to you." (John 15:3) When Jesus speaks, his very words make us squeaky clean. They shine ... and so do we.