Sentence:  No. 24. ¶ If your adversary make a false move, <WSD>castle</WSD> improperly, &c., you must take notice of such irregularity before you move, or even touch a piece, or you are no longer allowed to inflict any penalties. 
Meaning of the word marked with <WSD> tags:  To move the king 2 squares right or left and, in the same turn, the nearest rook to the far side of the king. The move now has special rules: the king cannot be in, go through, or end in check; the squares between the king and rook must be vacant; and neither piece may have been moved before castling.