Thanks for the feedback. Are you using mobile Safari? Can you try changing the pressure sensitivity slider to 0 percent? It might be an issue with wrong pressure detection. I've had to write some custom code for the native iOS version to fix it but hadn't really tested in the browser.
This is awesome, and I'm a bit surprised at the lack of more "dynamic" painting software in general (i.e where the paint keeps changing over time, affected by gravity, etc). I've made my own attempt at this[1] although my actual simulation code is quite primitive.
I have noticed that people oftentimes downvote because of disagreement, even when the comment seems to be okay (to my eyes at least). How about eliminating the downvote, leaving only the "flag" which makes it clearer that it should not be used for disagreement? It would also make comments more consistent with top-level stories (which I sometimes think of as "root-level comments".)