honeycomb in other places besides a cat

I was putting a new exhaust on my toyota 4x4 and i found a small honeycomb past the cat in the oem exhaust pipe right where the 02 sensor plugs in. Never knew they put one there, and it isnt real big mine was 2.5 '' in diameter. But if its got pm's like the other honeycomb it could add up for somebody who works on or has abundant exhaust pipes.