There are black pupils in them (4)
I believe the answer is:
eyes
If this is the answer, I'm afraid I cannot explain it.
Can you help me to learn more?
(Other definitions for eyes that I've seen before include "The first things children open on Christmas Day" , "Looks at carefully" , "They're said to be the mirrors of the soul" , "They look" , "Blemishes on potatoes" .)