how sharper than a serpent's tooth

The phrase "How sharper than a serpent's tooth it is to have a thankless child" is from William Shakespeare's play King Lear. It expresses the deep pain and anguish a parent feels when a child is ungrateful or disloyal. King Lear uses this metaphor to say that the hurt caused by an ungrateful child is more painful than a snake bite, emphasizing the intensity of the emotional betrayal and anguish he experiences from the ingratitude and cruelty of his daughter Goneril, and by extension, his other daughters. Lear's lament highlights the contrast between the natural expectation of gratitude from children and the harsh reality of betrayal. The serpent's tooth symbolizes something painfully sharp and poisonous, making the emotional pain of a thankless child even sharper and more wounding than a physical snakebite. The quote captures the heart-wrenching agony of parental disappointment and betrayal.