Simplify the following text for a Grade 6 native English-speaking person.
Original: In conjunction with a rook , the king may make a special move called castling , in which the king moves two squares toward one of its rooks and then the rook is placed on the other side of the king .
Simplified: With a rook , the king may make a special move called ` castling ' . This is when the king moves two squares toward one of its rooks and then the rook is placed on the other side of the king .