Only in the opponent's hand. I see now, thank you for the clarification.
In the discussion earlier, I did support being able to see which of your own cards the opponent has revealed, but if that's not the direction we want to take, I won't press for it.
For the purposes of a card like the one I suggested where it will reapply the Hide mechanic to (a number of) revealed cards in hand if there exist any, chosen randomly and not selected by the player, is it necessary to let the player know that there was any effect? If three of his cards were revealed and he didn't know which three they were, and then he played a card that hides again one of those three, he still wouldn't have to know which card(s) was affected.
If it's all too complicated, it's no big deal. I just thought the idea of an octopus using its ink spray to re-hide cards was fun.