It's the way he drags or pushes the chalk.
Angling it in the opposite way to normal makes it 'jump', creating the dots.
Indeed. Similar to a drum-roll. Or, probably more accurately, making that noise by rubbing your finger round a wine glass rim.
@AlexD started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
It's the way he drags or pushes the chalk.
Angling it in the opposite way to normal makes it 'jump', creating the dots.