what happens when you forget to say check in chess
Check (chess) In friendly games, the checking player customarily says "check" when making a checking move. Announcing "check" is not required under the rules of chess and it is usually not done in formal games. Until the early 20th century a player was expected to announce "check", and some sources of rules even required it (Hooper & Whyld 1992:74).
Knight (chess) The knight is the only piece that can move at the beginning of the game without first moving a pawn. For the reasons above, the best square for the initial move of each knight is usually one towards the center. Knights are usually brought into play slightly sooner than the bishops and much sooner than the rooks and the queen.