I noticed this last night. Alot of kitbashes have shown up recently with people drilling holes in their Classics Optimus Prime figures to have a place for the smokestacks/machine gun weapon. I realized that, in robot mode, if you put the red windsail back in the hole in his back, pointed down, there are two holes on its underside where you can place the smokestacks. I didn't know if many had realized this, since I hadn't seen a thread, and I felt a little bad people had kitbashed and customized so many innocent Primes as of late to do this, when it was all right there in the first place. I'll get a pic up as soon as I fix my digicam, but suffice it to say, it looks pretty awesome, IMO.