I put a piece of visco fuse in the hole in the end... so it "doesn't look suspicious".
Fictional scenario:
Just WHAT do you think would happen to you if you brought that to English class, and it had a fuse burning?
And you told the teacher: "Oh that's my chemistry project! Sorry. Guess I brought it in for *that* class, but inexplicably brought it to English class. Didn't expect the fuse to light like that."
Teacher: "What IS it?" You: "Oh, a plumbing thing. Complex. You wouldn't understand..."