H2O2 naturally breaks down into H2O and O2 (reaction: 2H2O2 ⇒ 2H2O + O2), but very slowly
The catalyst, KI, causes this to happen much faster, releasing lots of steam, oxygen, and heat
The oxygen bubbles are caught in the magic space liquid (dishwashing liquid) causing a big expansion
We ended up finding out that by adding heck tonnes more magic space liquid made the elephants toothpaste shoot up even farther than what we had originally.