Timing of Lupine Assault

What is the timing of Lupine Assault?

Does it follow impulse (i.e. if Lupine Assault is played, impulse dictates that the player whose turn it is discards first, then prey, then grandprey, then grandpredator, then predator)?

Or, is it simultaneous (i.e. players separate 5 cards from their hand, place facedown on the table and reveal simultaneously)?

I think everyone discards at same time