So maybe it's not so much a riddle as it is natural progression of events in a house constantly full of boys! Here we go...
1) An innocent marshmallow minding it's own business, what did it ever do?2) A, not so innocent, boy looking a bit mischievous!
3) A sling shot being stretched to it's extreme in the hands of boy.
4) Innocent marshmallow being shot over wall into family room where a friend lies in wait for said marshmallow missile to appear. (Marshmallow is directly above Noah's head, see it?)
5) Boy encourages friend to, "give it a try!" So friend launches one too! (See this one? It's just to the left of the heating register it had just ricocheted off of the ceiling.)