Check to see if your pencil tool is on Straighten mode and if it is then set it to ink (the way you get to this is with the option at the very bottom of your tool bar, click it and several options should come up)
I was hoping that this video would be a reference for people, so they could learn something. I prefer that people do their own animations rather than just using this one. But anyway, I've got the file and I can't stop you
Man, i really adore your effort and investment making all these effects and video guides. I´ve sat some hours on my sketchbook trying to draw organic lines...I still need some practise..but thanks for sharing!