Brush the jam over the top of each cooled cake with a pastry brush. Knead the green icing on a work surface lightly dusted with icing sugar. Roll out very thinly and cut out 12 rounds using a 6 cm (2½ inch) cookie cutter. Place a green round on top of each cake.
Take a small ball of icing in any colour – about 8 g (¼ oz) – and roll under the palm of your hand into a thin sausage about 12–15 cm (5–6 inches) long, tapering it to a point at one end and shaping a head at the other. Flatten the head slightly and mark a mouth with a small, sharp knife.
Roll out a little icing in a contrasting colour thinly and cut out small diamond shapes. Secure along the snake using a dampened paintbrush. Wrap the snake around a length of flaked chocolate and position on top of a cake.
Make more snakes in the same way, kneading small amounts of the icing together to make different colours, such as red and yellow for orange or red and white for pink. For some cakes, press the chocolate vertically into the cake.
Roll small balls of white icing and press tiny balls of black icing over them for eyes. Secure to the snakes' heads with a dampened paintbrush.