Something missing here...

So when I first got the car, I checked out the cabin air filter and saw signs of an obvious nesting of some small rodent... (small bits of foam and paper on the filter) but don't know think they are still in there. Then the other day I'm yanking the dash apart for some stereo work and I see what is in the picture. Guess I know where the foam is from... What else am I missing and where can I get it to replace it. I'm guessing a mouse since the droppings were pretty small.
Hopefully no other damage has been done...

 

I did just that after reading about others misfortunes. Here's how it turned out. Also dropped a few dryer sheets in the car and will be putting some humane traps in there tonight.