Inspecting 360 pre-cats - what to even look for?

Out of curiosity I popped out the O2 sensors on the factory headers and put a scope in there to get some photos of the pre-cats. From what I can see and what I know of what the outside of a catalytic converter should look like, they look perfect to me. I am curious though if there are any tell tale signs of impending failure that would be identifiable with a scope.

This is on a 2000 360 with 19,000 miles.

 

Probably not with a scope unless bits are missing, which they are not. The first sign to worry about is if the cat core is rattling in it's housing. When I changed my 430 headers one pre-cat was loose. Had to shake the header to hear it. Never heard it on the car though. I believe that was stage 1 of slow failure.