What’s the best reaction you’ve ever watched take place ?

Question: What's the best reaction you've ever watched take place ?
- Keywords:
  chemistry,
  experiment
Asked by Dannylewlewbeth to Matthew on 17 Nov 2014.
- Matthew Camilleri answered on 17 Nov 2014:
  
  Personally I really enjoy watching fireworks, and they are controlled reactions for everyone to enjoy.
  
  When it comes to lab reactions I have had the pleasure to play with sodium a couple of times, and it is so much fun watching it fizz on the top of the water.

Question: What's the best reaction you've ever watched take place ?