Take a look at what happens when you brush nitrogen triiodide with a feather

The mere brush of a feather on nitrogen triiodide will result in a rapid and dramatic explosion. But why is this substance so reactive?

The compound nitrogen triiodide is extremely unstable due to its structure. It's formed of a nitrogen atom and three atoms of iodine, which all bundle closely together on one side of the nitrogen. The close proximity of the nitrogen atoms, which are much smaller than the iodine, creates "bond strain," which results from the electron-electron repulsion of atoms that are too close together.

The potential energy this strain creates makes the molecule extremely unstable and prone to be more reactive. In this case, extremely reactive. When it comes into contact with even slight pressure the molecules fall apart, creating a dramatic chain reaction that produces a vibrant plume of purple iodine gas.

Let The Royal Institution walk you through the minefield that is nitrogen triiodide and show you the reaction in awesome slow-mo footage.