My opponent has an active Gallade and declares the attack Psychic Cut. Base damage is 60 and he flips 3 cards for an extra 60 to total 120 damage. My Gallade who is on the receiving end of this very nasty attack, has the full 130 health points remaining. My opponent then says, I knock you out, picks up a prize, discards his supporter, and says go. All this is done very, very fast (you all know what I am talking about). After you do the mental math in your head, you realize that you are not knocked out but have 10 HP remaining. The attacker says oh I need to flip one more prize card. Is he ALLOWED to do this without asking his opponent and why?