[EDITED] I just figured out how hurry ups work! And this may answer Wotto's question.
Shooting any major shot lights the red spider insert for that shot. Think of that as the "selector";
it indicates where the next "award" will go:
* Shoot Sparky to award knife switch insert for selected shot
* Shoot Graveyard to award cross insert for selected shot
* Shoot Snake to award snake insert for 3 shots (configurable),
or 2 shots if only 2 remain.
Once the knife switch, cross and snake are all lit, that shot is will start the hurry up - even if the spider insert is no longer lit because you shot something else. When your ball drains, all inserts will go out.
There's a catch to this: shooting the Graveyard will also select the Graveyard shot (light its spider).
I LOVE the way this works. While you're playing, you're building up inserts for hurry ups. This rewards long balls and gives you another reason to shoot Graveyard, Sparky and Snake. This also creates an interesting strategy: build up hurry-up qualified shots, and then start MB when you have more than one.
I have a feeling that "Seek and Destroy" may have something to do with all of this too, once it's implemented. Or maybe it already is?