While playing with Nugget today, we were switching between fetch and basic obedience commands. She always looks me in the eye when we're playing, so when I told her "drop it", I saw her pupils shrink a little, then dilate to normal as she dropped the toy.
It was neat, like she was registering what I said.
(Unrelated, but I'm going to start teaching commands with fruit/vegetable names!)
Have you noticed your dogs' eyes shrink/dilate when you tell them a command?