Sleeping with your eyes open

When I'm driving now, Evi's carseat is directly behind me so I can see Sierra on the other side if I turn around, but I can't see the baby. The other day in the car I was wondering if Evi was awake or asleep, so I asked Sierra if Baby Evi's eyes were open. Sierra responded emphatically, "Yes! Baby Evi is sleeping with her eyes open!"