On some motorbikes there is a device that lets air into the exhaust system to help cut down on emissions. This also creates popping and crackling on the way down the revs as a by-product.
It used to be on mine but I removed it when I had the bike tuned as it can mess up the fuelling readings and also adds unwanted weight.
The air that gets pumped into the exhaust is secondary air injection.
Our cars keep injecting fuel on overrun, this combined with ignition retardation during shifts is what causes the pops and bangs.
Most others cars cut fuel injection during overrun.
I don't think it has any anti-lag effects. The only benefit I have heard is that it provides cylinder cooling as the fuel is still washing through. That's the purpose of injecting fuel in over-run in race car applications.