The skull is controlled by three servo's giving it three degree's of freedom, it also has Led's in the eyes to add a dramatic effect [see the later blogs]
Degree's of freedom:
>Up/down
>Pan [side to side]
>Head Tilt
I'm not going to be putting a full wiring diagram because Charles Gantt did it so well in his blog:
Trick or Trivia Halloween Candy Dispenser #004 - Building The Candy Dispenser & Servo Coding
Wire it up to these GPIO pins on a pi model 2:
SERVOVertical = 26
SERVOHorizontal= 19
SERVOShake= 13
LEDEyes=06