Puzzle: Hanayama: Key Lvl 1

The Hanayama Key Puzzle, designed during the 19th century trend of British puzzles, presents two keys that appear to be unbreakable while joined together. However, these keys can actually be separated, making it a beloved choice among puzzle fans globally. Featuring top-notch quality and 6 levels of difficulty, including a Mensa ranking, this mind-bender is essential for trying out regardless of your expertise. Can you decipher the secret behind the "engage" key term?