The size of our pupils can say a lot about how we're feeling. Some methods of marketing research relate the size of the pupils to the attractiveness of TV commercials, for example.
Greater sizes can indicate that the person is attracted, happy, or just likes what it is seeing. Smaller usually denote the opposite, and that kind of control can be very useful in close up shots to help indicate how your character is feeling.
003-Pupils.blendfrom the book's support files. You'll see a rig to control the eyes and eyelids, with shapes applied to the bones. That's our starting point, as you can see in the next screenshot: