- A plastic cup
- A balloon
- A pair of scissors (And a grown-up to help with the cutting.)
Using the scissors, carefully cut off the bottom of the plastic cup - as shown in the image below.
Tie a knot in the end of the balloon, and cut off 1-2 centimetres from the opposite end of the balloon.
Stretch the balloon over the top of the cup and load up the marshmallows on top.
To fire, reach inside the cup and pull back the knot on the balloon. When you let go, the marshmallows will shoot from the cup!