This eye can serve either as Halloween decoration or as simple toy, it has eccentric mass inside which makes it go zig-zag when you roll it (sadly animated gif showing this didn't work when uploaded). Inside is CR2032 battery, 3mm LED and 47 Ohm resistor as shown in the image, when you press both parts together LED lights up. Parts are made out of red and transparent PLA. You can hot glue something heavy inside to enhance the effect.
The author hasn't provided the model origin yet.