Normal sudoku rules apply. Every 3x3 box contains one hidden 2x2 region called a Whisper Square. In a Whisper Square, orthogonally adjacent digits must have a difference of 5 or greater. Whisper Squares must not touch each other orthogonally, but they may touch diagonally. Within each cage, the sum of digits inside Whisper Squares equals the sum of digits outside Whisper Squares.