Move your mouse through a cloud (the disk is the "ship"). Tiny particles get shoved, the local concentration drops, and the cloud tears, then the pieces drift and stay torn. That's the H2O model: each particle carries itself, density is just how many are in one spot.
reform = 0 means torn cloud stays torn forever (pure break). Nudge it up and the pieces slowly re-amalgamate toward home, like water beading back together.