When John's daughter shows him the video footage she has made, the scroll bar under the video (and the display showing the elapsed time) suddenly goes from twenty-something seconds to more than one minute, and then goes back again, with nobody touching "rewind" or anything similar.
In order to help save the day, the hero and heroine come across the idea of using shredded aluminum cans in order to disrupt the bats' "radar". They get this idea after a stoner teenager points out that he avoided a ticket because the cans on his dashboard screwed up the trooper's radar. The problem is, bats don't navigate using Radar (i.e. radio or light waves bouncing off of objects); they use Sonar (sound waves bouncing off of objects), which wouldn't be adversely affected by metal. While the confetti storm could conceivably have been confusing to the bats, it wouldn't have "blinded" them the way the movie implied (considering the fact that bats are used to flying in swarms or through leafy wooded areas, so it's not like a bunch of fluttering objects would completely disoriented them).