Found these inside my cat-back exhaust, Anything familiar? Are they broken parts of the cat?

 

Yes, drop it and inspect it, be sure it's not restricting your exhaust.

 

yep, definitely ceramic converter material

whether it came from the current one or a previous one might be in question unless you’re the original owner and know for sure.

there are two cat bricks. The front one is easy to see looking into the exhaust manifold attachment flange end. The one in the rear not so easy without an insertable probe type camera viewing devicet

 

Shards of Rhodium and Platinum! Substrate structure compromised. Time to decat or new cat.

 

your cat seems to have used up all 9 of its lives.