I remember playing a game on my friend's computer, possibly an old Amstrad with a black and white screen, that involved a square that had a little 'creature' i.e. a dot, bouncing around in it. You were a cursor outside the box, and had to draw a straight line across the box, trapping the 'creature' inside half the box. Half the box would then turn black, and you'd have 'saved' 50%. The higher the levels got, the higher percentage you would have to save. I've drawn a mock up of what it looks like (in my hazy brain, anyway!). Does anyone know what this game was called? Or, more excitingly, where I could get hold of a version of it? Thanks for any clues you have.