Bonus points:
Locate the rooms in the ships that contain green faces on the floor.
Collect 500 points for killing them, then wait until they re-appear. Kill them
again for another 500 points.
Temporary invincibility:
Wait until 272, 267, 232, 222, 171, 161, 131, or 121 is displayed on the
counter, then collect the boxes with the question marks from the ships.
