Exhaust question

I have a 2006 M5. I know there are cats right off the exhaust manifolds, but about 2 feet down the pipe on each side is about a 1 foot section, like another cat, but there are no sensors, nothing. I know there is a resonator down closer to the mufflers, where the factory H pipe is. But what the **** are the two pieces in between the cats and the resonator....??