Special "Vaseline" 1 in. diameter marbles fit into a skull's eye sockets.  When these marbles are illuminated with black light LEDs located in the skull cap space, the whole
marble glows green with a beam of light making a "slit like" appearance through the
center of the marble/s.  These marbles are available on Ebay.

Here's the look of a single marble, illuminated by:

Natural light                                                            Black light