This quote comes from Act 1, scene 4 of William Shakespeare's King Lear as the titular Lear laments that his children, more specifically his daughter Goneril, are inherently ungrateful. Lear abdicates power to his daughters, only for them to disregard his wishes. He poignantly uses the image of a serpent's tooth and bemoans the fact that his power hungry children have no sense of gratitude or familial loyalty. While Lear is referring directly to Goneril and attacking her lack of character, the metaphor extends to his squabbling family. Lear wants his family to be respectful, and their general apathy toward his well being in conjunction with their greed for power make them ruthless entities. Therefore, he compares them to dangerous serpents, which carries an additional evil connotation in that the serpent in Western culture is often associated with Satan.