DIY: How to make a crossbow that shoots marshmallows

You've just hosted a great summer cookout, complete with s'mores for dessert. The next morning, however, you realize that you have a bag of marshmallows left over. What do you do with them? You could use them as a quick frosting for your freshly baked cupcakes. You could use the marshmallows to separate your toes during your next home pedicure. Or, if you're like Steve Ramsey from Woodworking for Mere Mortals, you construct a crossbow to fire marshmallows throughout the neighborhood.