White trails / smoke appears when playing!
These trails are a feature called smoke and can be used to draw on your playfield for novelty's sake. Anybody who is spectating you can see this smoke as well. Draw pretty pictures, or phallic objects to the amusement of your spectators!
The default keybinding for this feature is C, and needs to be held down in order to function.
How do I remove it?
If the smoke appears when you don't want it to, go to main menu and open the options menu from there, find the button named"Key Bindings" and click it to bring up the keybindings menu. In there, look for the entry named Smoke and change key used for smoke to a different key.