I suspect that's for the Automatic High Beam system, since I think the sensors above that are for rain detection.

I can't remember if I pulled that cover and normally would take a moment to do so just to pass along the information, but it's hotter than (your simile here) outside.

 

Ha, the hotnmess.
That makes sense; I do have the auto-beam function. The plastic trim is all one piece, wrapping nicely around it.

 

I gave it another shot and was scared I'd break it. If anyone has a way to open my kind of rear view mirror, please let me know. Thanks!