After drawing, P1 folds their image back to hide the image, leaving just a few millimeters for the next person:
Player 2 takes the paper and draws a "middle" - often a torso - by connecting to the lines made by P1:
P2 then folds their image back, leaving a little left for the next person:
After P2 folds their portion back, Player 3 uses these marks to draw the "end" - often legs:
After P3 is done, everyone gathers around to "ooh" and "ahh" at the final result:
The number of participants for one corpse is not regulated at all, so all combinations are accepted.
The head-torso-legs method is just one way of composing an EC.
Variants involve horizontal layouts, collage, photography, just about anything.