Library strangeness

Mom told me this story: Yesterday there were two teen girls blocking the entire magazine section. They were constucting something out of wood, paper and what appeared to be those pool noodles. It had a helium balloon attached to one side. At one point a hammer and a screw driver were used. The pair also had a hot glue gun and were frantically gluing when mom told them the library would be closing. It had been busy and no one had complained about the girls so she had just left them alone, but told them to please not hammer so loudly in the library. As she drove away, Mom noticed the two girls outside the library still constructing whatever it was. She never figured out why the girls thought it would be best to construct a big five foot tall whatever at the library. Couldn't it have been done at someone's house. The girls just gave non-commital answers to these questions and apologized for doing this in the library.