Two illusions in one!
The first illusion is created by using the illusion knitting technique so that you see squares when you look from a distance, stripes when you look closer and circles when you look from an angle. The second comes from the perception of 25 different shades when the hanging only uses five different yarns. This effect is only seen when the piece is viewed from directly in front.
What you see varies according to the lighting. At times you can also see circles that appear to be embossed on the background. It is very difficult to capture all these effects on camera. The hanging needs to be seen in real-life to appreciate how much it changes.
Note: The title is with apologies to Roald Dahl, who invented SQUARE SWEETS THAT LOOK ROUND in Charlie and the Chocolate Factory.
Note for knitters: This pattern is not recommended for a first illusion knit. It is more complicated than the others because of the number of balls of yarn involved.