Do you feel that sometimes you have nothing to talk about with your friends? Do not worry! This trick is a good chance to show your friends something they may not know. It is very cool indeed, and also very cheap and easy to do. If someone has a scientific explanation of why this happens, well, let me know in the comments.

Título en español: EL TRUCO DE LA VELA.
Este truco es una buena oportundiad para hacerlo frente a tus amigos. Es muy divertido, barato y fácil de hacer.

Link.