Zombie Infestation + Triskelion Question

[Polynomial P]

Here is the situation:

I attack with Werebear and other creatures and an opponent blocks one of the other creatures with his triskelion.

I have 3 cards in my graveyard, 4 cards in hand and a Zombie Infestation in play. I choose to discard 2 cards to infestation and then 2 more to infestation and my opponent tries to respond by pinging my werebear with his triskelion. I think that because discarding cards is a cost of infestation, by the time he responds with triskelion the cards are already in my graveyard and the werebear is a 4/4. Can someone confirm this?

Here is the Oracle wording of infestation:

Zombie Infestation 
Enchantment

Discard two cards: Put a 2/2 black Zombie creature token into play.



 

[Matt]

You are correct. The cards are discarded as a cost of ZI's ability, and costs cannot be responded to. As long as you have the cards to fuel this play, he cannot stop your Werebear from gaining threshold (threshold is a static ability and does not use the stack - it's "always on" or "alwasy off" and switches instantly between the two).