The term 'It's Slippery When Wet' can be summarized by two crossword solutions: SOAP (4 letters) and EEL (3 letters). SOAP is a substance used for cleaning, usually in the form of a solid bar or liquid. It is made from fats or oils combined with an alkali, such as sodium hydroxide. An EEL is a long, slender fish that lives in both fresh and salt water. They are known for their slippery skin, which helps them to move quickly through the water.