The inside of the mask is made to look like that. Its just an optical illusion, stare at it for awhile and tell yourself thats its made to do that and its just the inside of the mask using depth to trick your eyes.
The first part of the mask looks like it is rotationg counter clockwise, making it look like it extrudes. When you watch the second mask, you see it is rotating clockwise, so you just have to watch the first mask and tell yourself it is moving clockwise.
The reason it's screwing with your head is that the light source is moving along with the mask. This means that you can't see the shadows on the concave side of the mask. If you could see these shadows your brain would recognize that it is concave and rotating the opposite way it looks.
Don't believe me? Look at the shadows in the background.
Actually the light source might be at an angle so it doesn't even need to move in order to keep the whole concave section bright. The apparent shadow changes in the background might be due to exposure change.
This sorta reminds me of something my sister showed me. Look at a water fall, unfocus your eyes, after like 10 seconds look at the rocks next to the fall and they will move just like the water was. The cells in your eyes move with the falling water and the still move shortly after you gaze away, or somethin like that. Shes an optometrist so she knows all sorts of cool eye and light shit