Well, I know if this happened to me, we'd have a lot bigger problem on our hands because I'd definitely have wrecked the car and soiled the driver's seat.

On a more technical note, I don't think there would be access via the shift linkage unless there were a lot of missing parts.

I'm wondering if it was able to drop in from the cowl through an air vent? Although it seems the cabin air filter would've stopped that... Perhaps it was able to push its way through the weatherstripping?

Or.... have you made anyone angry lately?

I am currently working on a car that sat for several years in a field; there are snakeskins all over the engine bay but none in the car that I've found (yet).