What are the holes in my exhaust?

[rallen5]

I recently installed a full Arrow exhaust on my 07 S2R. Last night I was out on an 200 mile ride and at the half way point I started feeling a pulsing on my left heel so I checked and I've lost the brass plug for the rear cylinder's header bung.  After riding for an hour I realized I had also lost most of the popping from the exhaust when I roll off the throttle. So I'm wondering why the holes are there and if I should replace the plug?


Richard

[xcaptainxbloodx]

replace the plug, its used for tuning the motorcycle at services.