Included in this EUG magazine is this new demo from Explosm.Net called 'Back In The Day'. For those of you who do not download the companion disc, the above animated gif shows it in action on the BBC/Electron.
The "instant animation" effects of the different guys appearing (without having to load in a different image each time) is achieved by using colour-switching. The picture itself is loaded in Mode 2 which allows for sixteen colours but by using a VDU 19 command, all colours can be either 'whited out' or made to appear as appropriate.
To see exactly how it is achieved, you can try *LOADing in the picture with the following commands:
MODE2:*LOAD D.BACK2 3000