Mad_Cyril sorry…
Hugo and Amps each have half a square cheese cake. Hugo suggests that Amps shares his cake with his sister Anne, Anne’s mother’s husband and his husbands cat.
Anne cuts each slice to have the same amount of cake, using the perimeter of the cake. (It’s essentially the same as dividing a circular cake into five slices). Since the perimeter of the cake is 20 units (as marked by Hugo’s brother, Alan), then each of the five slices must have 4 units of edge. So, we choose a point on the perimeter and then mark all the other points four units along before shoving it up Alan’s ringer.