I think that when you break it, it releases chemicals and makes it glow when you snap it.
What I think now (after hearing others’ ideas)
Fragile canisters inside glow stick which when you break it to the extent it breaks and explodes with the glow. And the sound gives away quite a big clue because when you snap it you can hear glass breaking into shards.
What I think now (after seeing Miss C cut open the tube)
My prediction was right after getting the full information from watching Miss C and listing to the others in class.
What I think now (after researching)
After researching I now know that a glow stick does the same basic thing, but it uses a chemical reaction to excite the atoms in a material.