It's a metal shroud that envelopes the regular muffler to stop the radiant heat damaging the plastic all over cover.

The fancy cowl amounts to a flimsy cleverly designed veneer that's effective in giving the feel that there's a giant hi tech engine under there as you push it around.
It's enjoyable being fooled by it though. It's very stylish looking from certain angles. No wonder it won a design award.

Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!