"Here's looking at you, kid."

Ok, in general you only have two eyes. This might be sufficiant, but why not have some spares? Print your own eyes in your favourite colour.
And there is more - these eyes not only look good, but you can open them. Only a few rotations and you can place some candy inside as a spooky giveaway.

Printing is quite easy: Print everything with three walls, four tops & bottoms and 8% gyroid infill. Support is not needed. For a neat tumbling figure effect you can make the bottom half extra heavy by printing it with 20 tops & bottoms. Then the pupil will always face up.

After printing glue the iris and the pupil to the top half. Screw the thread in one of the halves and close the container by screwing the other half to it. For an optional reflex effect draw a single white dot on the iris. Just use white paint or a white permanent marker.

Disclaimer:
This work by blecheimer is licensed under CC BY-NC-SA 4.0
You are not allowed to copy this model to other 3D printing websites without my permission.