This is a hollowed out light bulb filled with fluorescent liquid and two UV leds plus one red led immersed in the liquid. When turned on the light bulb flickers for a while then starts to pulsate randomly with the UV leds giving a spooky but rather nice look.
The bulb is held to the box by two small magnets that also is used as contacts for the power to it.
I got the inspiration for the project when I stumbled upon a web site describing a similar project. imakeprojects.com/Projects/glow-crystal/
In the last step of this instructable there are two videos of it in action.