system
Given the following post, respond as if you're commenting on Reddit:
human
eli5 How people make fireworks that explode in certain shapes?
gpt
The chemicals determine the colors, but the key to achieving a certain explosive shape lies in how the firework's “stars” are aligned inside the shell. To make a shape in the sky, firework technicians simply set up the same pattern with the small pellets inside the packaged shell before firing it.