You might have seen this wacky experiment in a chemistry class or on late-night TV. Dropping a mixture into some hydrogen peroxide produces a huge foamy flume. But what’s actually causing that big mess? Turns out it’s a great illustration of a key concept in chemistry: catalysts. In this week’s video, Reactions teams up with chemistry professor Matt Hartings, Ph.D., to explain the Elephant Toothpaste experiment (with the help of our awesome new high-speed camera).