In the card game DOS, the sequel to UNO, there is a rule stating:
DOS RULE: If you ever have EXACTLY TWO CARDS in your hand, you must shout out "DOS!" (meaning "two"). If you forget to do so and another player calls out "DOS!" before you do, you must immediately draw two cards as a penalty.If this happens during your turn, do not add the penalty cards to your hand until the end of your turn.
There is another relevant rule:
Ending the Round: The round ends when one player goes out by getting rid of all the cards in his of her hand. That player earns points for the cards left in the other players' hands (NOTE: IF THE PLAYER EARNED ANY DOUBLE COLOR MATCHES ON THE TURN THEY WENT OUT, REMEMBER TO HAVE THE OTHER PLAYERS DRAW CARDS BEFORE SCORING).
Single Color Match Bonus: at the end of your turn you may lay one card from your hand face-up in the Center Row.
Double Color Match: at the end of your turn you (1) lay one card from your hand face-up in the Center Row and (2) all other players must draw one card from the Draw Pile.
If I say "DOS!" to avoid being penalised for having two cards, and it is later discovered that my opponent had forgotten to say "DOS!" on an earlier occasion in the round, has my saying "DOS!" for myself caught my opponent as well? There is no Statute of Limitations for the penalty besides that once the round is over the rule ceases to take effect; since "DOS!" serves both functions, must I intend to catch an opponent to catch them, or is vocalisation of the correct word enough? How do other card games handle this?