Homemade slime, all part of the Hip Science Show.
When carbon and hydrogen bonds are ripped apart, it generates a high amount of heat. Enough heat to create a very hot fire.
That fire then ignites a piece of nitrocellulose string. The string flashes due to being nitrated, which means it will produce its own oxygen when burning.
The string is the only thing holding a ball in place. So when the string burns, the ball rolls down the ramp and into the cup.