Insulation Blowing from vents in '05 Corolla

NEWBIE question:
In the past few days I've been getting what looks like pieces of insulation blowing from my air vents. I'm concerned I've got a field mouse in there. How do I get the bugger out? How do I access the air intakes and other air flow paths?
Thanks!!!

PS - Does anyone know of any links to pictures or diagrams of the ventilation system?

Is the insulation white color?
The air that come out from the vent, does it have a wet smell.
There is an air filter under the hood. (I don't think that's the cause)
There's another filter behind the glove box, maybe it got wet and dry up afterwards and now is coming out from the vent in small pieces.

Is the insulation white color?
No - it was mostly gray and black. I checked and it wasn't from the air filter.
The air that come out from the vent, does it have a wet smell?
No - there was no smell at all.
There is an air filter under the hood. (I don't think that's the cause) There's another filter behind the glove box, maybe it got wet and dry up afterwards and now is coming out from the vent in small pieces.
I took it in to the shop this morning and they pulled the blower motor. They didn't find a nest, but did find some insulation chewed by a mouse or some other rodent. On closer inspection, we saw that 3 of the cross bars on the plastic grill for the defroster vent inside the passenger compartment had been chewed through on the drivers side. The shop manager said that he'd seen this happen from the engine compartment side several times before, but only once before from the passenger compartment side.

I picked up several mouse traps and set them in the garage. First time in the 16 years we've been here that an animal has gotten into one of the cars (that we know of anyway). I learned my lesson - from now on, I set traps every fall when the temperature drops below freezing. Hopefully, my story can help someone else before they have the same problem.

Very interesting.