Lovely shots of Lucy. My 3 boys have a cat flap that works with their micrchips. Ripley hated it at 1st- we think the clicking noise- after using the old one and refused to use it so for about 3 months we had to keep a bedroom window open for him to come in and out but finally he accepted it and began using it!
Excellent pictures - as yellodog says, its the eyes.
I'm glad your cat flap is a sign of freedom. For our two at the moment I'm afraid the cat flap is an instrument of repression. They are both cowering away in corners afraid of the stray cat that has taken to coming in. We're seriously considering getting a new flap fitted that's triggered by their i.d. chips.