99 [but not quite that many] coloured balloons

i was sitting in my room, working on my computer, when out of the corner of my eye i saw something move past the door. Seeing as no-one else was home, except my sister who was in her room downstairs, i was slightly disturbed - and after a double take it turned out there was a bunch of balloons just casually floating through the house, about midway between the floor and the ceiling. I thought this was hilarious, and i went downstairs to tell charlotte. while recapping my story - trying to make floating helium balloons sound funnier than they were - my peripheral vision continued to be exercised, and i saw something else out of the corner of my eye. This time it was a moving shadow on the ground, outside the window. On further investigation, i discovered that this shadow was in fact being cast by a bunch of balloons, that had drifted out an open window on a draft...