Things were progressing just fine (save for the catchy!folktale music that was constantly playing over and over), until...

Balloons that had been deflated and just lying harmlessly along the tracks began to inflate. First, there were only a few blowing themselves up and passing right over the students' lines of vision.

Then...there were many. Not only that, but as soon as they got just at eye-level, they began popping and releasing shaving cream into the air--and onto whoever happened to be unfortunate enough to be floating nearby.