*new words of the day •friction — the force that works against an object as it slides along the surface of another object or moves through a liquid or gas •discoloration — a change to the original colour of something that makes it look unpleasant or damaged •clog — a change to the original colour of something that makes it look unpleasant or damaged •black head — a very small, dark spot on the skin caused by a blocked pore (= small hole in the skin's surface) •lo and behold — something that you say when you tell someone about something surprising that happened •on edge — nervous and not relaxed •hoarse — (of a voice or a person) having a rough voice, often because of a sore throat or a cold