According to what I heard it creates a paradox because; if his nose doesn't grow he would be lying, so it would grow, and if it grows he would be telling the truth, so his nose would grow when he told the truth, which is only supposed to happen when he lies.
That's not what would happen though. For that particular scenario playing out you can prove his nose didn't grow when he told the truth because he said "now", or his nose would grow "now".
His nose not growing had to happen before lie occurred, so the lie and his nose growing would be considered after his nose didn't grow, which