Electricity can be scary!! And, dangerous. But, you needn't worry about that with LEDs. LEDs run off low-voltage DC (typically 1.5 volts) and are a breeze to work with. They come in a multitude of colors to suit anyone's needs and they are cheap.
The easiest way to do this is to simply pair an LED with a 1.5v disposable watch battery. Attach the positive LED lead (the longer one) to the positive side of the battery, then attach the negative lead to the negative side of the battery. Press the LED leads to the battery, and the light should come on. Wrap them together with tape and you're good to go. The LED can stay lit for up to two weeks before the battery runs out.
This method works well with an Bucky Adult Skull. Simply, pass the LED leads through the openings in the back of the eye sockets and attach them to the battery. A great enhancement to this is a .75 or 1 in. acrylic sphere available from Tap Plastics or many craft or hobby stores. A good example of this are the eyes of our Reaper Guardians.
With some basic knowledge of electricity, you can get pretty fancy with LEDs. And, with some simple kits you can buy on-line or at a hobby store, you can even make them blink, flash, and fade in and out. And, placing pairs of these in your bushes will give your Halloween guests the sense that they are being watched by critters.