When this card’s effect is active, both Decks are flipped upside down, and now the face of the top card of the Deck is showing.
If a card effect requires a player to shuffle their Deck, it is shuffled and cut face-down so the cards are not seen, and then placed face-up in the Deck Zone.
If a "Parasite Paracide" is face-up in your Deck before this card is activated, it will become face-down once this card is active. Its effect will still activate when it is drawn.
If 2 copies of "Convulsion of Nature" are active, the Decks are still upside-down (they do not revert to normal).