Needed a thread to post this in. Yes, yes I am a nerd.
www.sciencealert.com
The Pupil in Your Eye Can Perceive Numerical Information, Not Just Light
You might know that the size of the pupils in our eyes changes depending on how well lit our environment is, but there's more to the story: Scientists have now discovered that the pupil also shifts in size depending on how many objects we're observing.
www.sciencealert.com