Funny cat story: Our orange and white female, Tigger, likes to curl up on top of my husband's computer monitor while he works on the computer. Over the weekend we got a new computer and moved the one she sleeps on into the kitchen. We wondered how she would react to her monitor being moved, since the new computer has a flat screen!
Sure enough, she attempted to access the top of the flat screen and ended up doing a "kilroy". Her front paws and eyes were visible over the top of the screen, but she couldn't figure out where the rest of it went.
A definite "you had to be there" moment. The outraged look on her face was priceless.
You've seen this, so you can relate. Their only access to the top of the monitor was from the front and, from there you can't tell if there's anything behind the screen, so I'd be sitting here, a cat would walk up, take a look at me, look at the top edge of the monitor and jump off into oblivion.