 guided
 stop when animation loops
 persistent
 alien projectile
 affected by gravity
 no horizontal error
 no vertical error
 can toggle control panels
 positive vertical error
 melee projectile
 persistent and virulent
 usually pass transparent side
 sometimes pass transparent side
 doubly affected by gravity
 rebounds from floor
 penetrates media
 becomes item on detonation
 bleeding projectile
 horizontal wander
 vertical wander
 affected by half gravity
 penetrates media boundary
