Teaching grandmother to suck eggs is an English language saying meaning that a person is giving advice to someone else about a subject about which they already know (and probably more than the first person). "Egg sucking" removed the egg contents while preserving the shell intact. Two small holes were made on the ends of the egg, and the contents sucked out. The shell could then be painted or otherwise used for decorative purposes without it becoming rotten and smelling bad. == Origins of the phrase == The origins of the phrase are not clear. The OED and others suggest that it comes from ...