Three prongs at the right end, two at the left. Look at either end on its own and nothing is wrong. The trouble is in the middle, where no line settles how many prongs there are, so both readings hold. That is why the figure carries no fill: filling it would turn the middle band, a prong on the right and a slot on the left, into a visible seam.
The panel names at the top right open the fork, motion, and color panels. Fork sets the number of flat prongs, the thickness and spacing of the prongs, the length of the figure, how much of it reads as round, how much reads as either, the line weight, and how much of the screen it fills. Add one flat prong and the round end gains two. Motion sets the speed and width of the light that crosses the figure, and whether it runs. Color sets the line, the light, and the ground.
Drag the stage to move the figure and use the wheel to zoom; the field at the bottom right takes a zoom value too. Double-click a panel title to switch how the panels are laid out. In the movable layout you drag panels wherever you like and keep several open at once; in the fixed layout a single panel sits in the top right.