A Spiral Optical Illusion (Hard)

On your scrap paper, draw a border round the edge. Then divide your paper in to 4 triangles using two diagonal lines across the middle. Choose one of your triangles to practise the spiral pattern in. Starting from one corner carefully start your triangular spiral, draw a straight line next to the edge of the triangle all the way up until you hit the other edge of your triangle. It should end next to the opposite corner of the triangle. Now starting from there, draw your next line next to the second side of your triangle again all the way to the opposite edge until you hit the edge just next to the corner. Now do your third line from where your second line ended all the way until you hit the third edge of your triangle, ending next to the corner.

Stay as close as possible to the edges so you only leave a little gap between your lines. You should end up with a slightly smaller, tilted triangle inside your original triangle. Now repeat the same process inside your new triangle, making sure you stay as close as possible and hit the opposite edge next to the corner. Keep going until you get right in to the middle.