An adult separates the egg carton into individual cups. Paint the outside of each cup black and leave them upside down on a sheet of newspaper to dry, about 25 minutes. They should be fully matte with no white cardboard visible through the paint.

An adult cuts bat wing pairs from the black card: each pair is a simple double-crescent shape, widest at the tips, about 8 cm across. A child can colour these in with black marker if the cutting is done ahead.

Once the cups are dry, glue a wing pair to each side of the cup near the flat open base (which becomes the top of the bat). Hold the wings against the cup for 30 seconds each until the glue grips. Glue two googly eyes on the curved closed end of the cup, which is the bat's face.

An adult uses a hole punch or a sharp pencil to make a small hole in the top centre of each bat. Thread a length of black yarn through the hole and tie a double knot inside the cup so it does not pull through. Cut yarn pieces at different lengths, from about 10 cm to 40 cm, so the bats hang at different heights.

Tie the other end of each yarn piece to the twig or dowel, spacing bats evenly. Tie a loop of yarn at each end of the dowel for hanging. The mobile is complete when it balances and the bats spin freely.