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Finally figured out how to zap the gumball bombs.

I can't find any manual on the net, but this is what I figured out:

CTRL+K for keyboard, S/F for left right, D for stop, E/C for factory speed up/down, Return for crosshairs, Space for flip valves
CTRL+J for joystick, button 2 for crosshairs, button 1 to flip valves.

When an exploding gumball shows up there's a warning sound, locate the bomb, bring up the crosshairs and put the crosshairs in contact with the bomb and it will be zapped.

The exploding gumballs don't show up until Thursday.

The crosshairs initially appear over the corkscrew so if you can make the bomb go up the corkscrew you can just activate the crosshairs.
There's also a flashing countdown timer for the bomb in the upper left and you may be able to wait for it to go up the corkscrew.

A pretty good strategy is to use the left chutes as much as possible early on as you can clear the gumball out quickly. If you let it take the long path you have to keep an eye on it and it gets hard to track it with the incoming gumballs. You have to ramp up the speed to keep up with the quota, but don't set it too high that you make mistakes and see the quota get bigger.

edit: I thought I was doing pretty good to get to thursday, check out this longplay