Harry only exists when viewed from the side.
From the front, he disappears.
At first, married couple Pat Ashforth and Steve Plummer were interested in mathematics and knitting, and they created designs combining math and craft. Then they discovered shadow or optical illusion knitting.
Mr. Plummer explains how it works:
In illusion knitting two colours of yarn are used to create alternate ridges of knitting, a dark coloured ridge followed by a light coloured ridge. Areas of dark or light can be brought into the foreground, when the piece is viewed at an angle, by using garter stitch for that particular part of a ridge and stocking stitch for that portion of the preceding ridge. When the piece is viewed from directly in front only stripes of colour should be seen.Harry Potter Illusion Knit
Leonardo da Vinci's "Lady with an Ermine"
More examples and videos can be found at their site Wooly Thoughts>>