At first glance this animated gif doesn't look particularly unusual or much of an illusion. Just a view of a table in a corner panning up and down.
But when you find out that it is not four different views but the same picture just moving up and down, now it looks strange.
The secret is that we have moved the picture up and down whilst keeping the wallpaper pattern at the same level and then cropping the top and bottom. - Spyman.
Original image source unknown