Here's the story:
I was installing the K&N air filters in my Z
I took this nice little comparison picture of the new filter on the left vs. the old filter on the right. The passenger side filter had one leaf and a little bit of styrofoam in it.
Well lo and behold, I take the driver's side filter out and found like
HALF A CUP OF DOG FOOD IN IT 
We haven't had this brand of dog food in years, and we never eat Smarties candy. I was laughing hysterically. Who knows how long that's been in there