I would say the correct response is even stronger. Dummy is not only allowed to point out the irregularity, dummy *must* do so and may not permit declarer to revoke from dummy. This is based strictly on the Laws and does not require any Committee interpretation in support. The reason is that Law 44C provides, "In playing to a trick, each player must follow suit if possible. *This obligation takes precedence over all other requirements of these Laws.*" Dummy is a "player" under the Laws. See, e.g., Law 9B, which refers to "Any player, including dummy." Therefore, dummy is subject to the obligation under Law 44C to follow suit if possible, and this obligation takes precedence over *all other* requirements of the Laws. Dummy's duty to follow suit therefore trumps (ha ha) dummy's obligation to refrain from participating in the play, to avoid pointing out irregularities once they have already occurred, etc. So while dummy should remain silent after most irregularities (e.g., if declarer calls for a card from dummy when the lead is in declarer's hand, dummy should just play the card without comment), if declarer tells dummy to revoke, dummy must object.