Noticing Movement

The Pine kids were excited to see something different set up in the classroom today that they have never seen: an overhead projector! Different colored round plastic disks were spread out across the flat surface. Both F & W started moving the disks around in different patterns. At first, each child worked side by side creating different patterns and designs without looking up at the projected image.

Then, F began moving pieces around individually and realized what he was moving on the surface of the projector was also moving up on the board ahead of him. 

He placed disks under each finger and began moving his hand around. It looked as if his hand was ice skating across the glass top. He giggled as the pieces he moved with his fingers were also moving on the board straight ahead. 

J & M noticed this from across the room. 

"Look, it's moving around!"

"Yeah, when I do this here, it's doing it up there too."

"My different colors are going all around, but I can't see some of them when I move them."

J ran into an interesting problem... some of the disks she was playing with on the flat top were visible when she looked at them from above,but they weren't visible when being projected. 

"What happened to them, I can't see them up there!"

She also noticed that the pieces she did put down were not always showing up on the same side in which she laid them down. 

"I put it here, but it's way over there!"

Why did the projector do that? Why does the image seemed to be reflected?