Thanks, yes thundermugs they be! Notice the serial fusing setup. I read that if they were set up on a hard surface such as brick road, a powder train past each of the vents would be used to get the serial firing.
Obviously that'd be difficult or impossible on grassy or overgrown earth, thus they are using something like quickmatch rigged to allow the advancing burn front to move past the vent toward the next mug before firing. That would keep the fuse from being blown out of the remaining mugs before they could fire.
